A recent study found no evidence that circumcising newborn boys increases their risk of developing autism spectrum disorder. The findings, published in JAMA Pediatrics, may offer reassurance to parents considering the procedure or whose sons have already had it. The researchers also found that acetaminophen was rarely given to the infants, making it unlikely that the pain reliever explains any connection between the procedure and autism.
Autism spectrum disorder is a neurodevelopmental condition that involves differences in how a person interacts socially and communicates with others. It also typically involves repetitive body movements and atypical responses to sensory input. The diagnosis relies on clinical assessments of a child’s behavior and development.
Over the past few decades, the rate of autism diagnoses has grown considerably. For example, the Centers for Disease Control and Prevention estimated that about one in 150 8-year-olds had an autism diagnosis in 2000, compared with one in 31 in 2022. Experts are still working to figure out how much of this increase reflects a true rise in the condition, as opposed to better awareness and changes in how doctors screen for it. Regardless, this trend has prompted scientists to look for environmental factors that might interact with complex genetic predispositions.
One consistent feature of autism is that it is diagnosed much more frequently in boys than in girls. As noted in a 2022 review of sex differences, this disparity may partly reflect differences in how symptoms present and are recognized by doctors. However, the higher prevalence in boys has also motivated experts to investigate early-life exposures that only apply to males. This includes neonatal medical circumcision, a common surgical procedure involving the removal of the foreskin covering the tip of the penis shortly after birth, which is performed on about half of newborn boys in U.S. hospitals, a share that has been declining in recent years.
The research, led by Monica McGrath, a research professor in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health and director of the Environmental Influences on Child Health Outcomes Data Analysis Center, examined whether newborn circumcision is linked to autism. In recent years, public speculation has circulated suggesting that the physical stress of the procedure, or the acetaminophen (the active ingredient in Tylenol) provided for pain relief, might contribute to autism.
In October 2025, Health and Human Services Secretary Robert F. Kennedy Jr. said at a Cabinet meeting that two studies showed boys circumcised early had double the rate of autism, and he suggested Tylenol given for pain was the reason. Media coverage of the remarks resurfaced two older observational studies: a 2013 analysis that compared circumcision and autism rates across countries and U.S. states, and a 2015 study of Danish health records that found a 46 percent higher risk of autism among circumcised boys.
“We knew we had the data to help investigate this question,” McGrath said in a news release from Johns Hopkins.
The authors of the new study pointed out that those prior reports suffered from potential biases. For example, in places like Denmark where circumcision is relatively rare, the procedure is mostly performed for religious or cultural reasons. This means that unmeasured factors, such as differences in when and how certain communities seek health care, might have skewed the older data. Because circumcision is routinely performed in hospitals across the United States for a broad range of families, the research team wanted to evaluate the question in a large, diverse American population.
To do this, the research team examined data from the Environmental Influences on Child Health Outcomes project, a national research initiative that tracks children’s health. The analysis included 2,771 male children from 14 different research sites across the United States. All of the children were singleton births, meaning they were not twins or triplets. If a family had multiple children participating in the broader project, the researchers randomly selected one child to ensure that shared family environments did not skew the statistics.
The scientists checked medical records to determine whether each child had been circumcised at a medical facility within 28 days of birth. They then tracked whether the children were later diagnosed with autism spectrum disorder. A diagnosis was recorded if a parent reported that a medical professional had identified the condition, or if there was documentation from standard clinical autism assessments. The average age at which the children received an autism diagnosis was just under four years old.
In addition to formal diagnoses, the team evaluated broader behavioral traits using two standardized questionnaires filled out by parents: the Social Responsiveness Scale, completed for 1,886 children, and the Child Behavior Checklist, completed for 1,880 children. The Social Responsiveness Scale measures the presence and severity of social impairments and traits associated with autism. The Child Behavior Checklist screens for emotional and behavioral problems, including a specific subset of behaviors that align with autism. Because these questionnaires produce scores along a range rather than a yes-or-no diagnosis, they could pick up milder autism-like traits in children who had not been diagnosed.
Out of the 2,771 boys in the study, 1,840 were circumcised before they were discharged from the hospital, making up 66 percent of the group. The remaining 931 boys, or 34 percent, did not undergo the procedure. Overall, 192 children in the sample had an autism diagnosis, which is about 7 percent of the group.
When breaking the numbers down by circumcision status, 6 percent of the circumcised boys had an autism diagnosis, compared to 9 percent of the uncircumcised boys. In other words, circumcised boys were somewhat less likely to be diagnosed. But the two groups also differed in other ways: uncircumcised boys were more often Hispanic, more often born in the West or Puerto Rico, and more often born prematurely or admitted to intensive care. After the researchers accounted for factors that could influence both circumcision and autism diagnosis, such as maternal education, geographic region, family history of autism, and parental age, the gap shrank and was no longer statistically meaningful.
The parent-reported questionnaires told a similar story: after adjustment, circumcision was not linked to higher scores on either measure. The researchers also checked whether the pattern held within subgroups, such as children from different regions, those born prematurely, and those admitted to the neonatal intensive care unit. In most of these checks, circumcised boys had similar or lower autism-related scores. One exception emerged among children born in the West, where circumcised boys were more likely to score in the elevated range on one questionnaire; the researchers suggest this isolated result may be a statistical fluke given the number of comparisons, noting it was driven by a single site.
The team also reviewed pain management records, which were available for fewer than half of the circumcised infants. Among those, only 4 percent received acetaminophen during the procedure, and about 7 percent of all circumcised infants received it within 30 days of birth. Most documented pain care involved a nerve block, an injection that numbs the area (72 percent), or a sugar solution given by mouth (59 percent), and some infants received more than one. Because acetaminophen was so rarely used, the researchers could not test its role directly, but they concluded that a pathway running from the procedure through the medication to autism is unlikely.
“Parents have been concerned about this potential circumcision-autism connection, but hopefully these findings may help allay their fears,” McGrath said.
As with all research, there are a few things to keep in mind regarding this study. The team noted that they had limited information on the participants’ health insurance status. Because insurance coverage can influence both a family’s decision to have a hospital circumcision and their access to developmental evaluations for autism, missing this variable could leave some untracked influences in the data.
The researchers also pointed out that they specifically evaluated medical circumcisions performed in a hospital setting shortly after birth. The findings might not apply to circumcisions performed later in childhood or those conducted outside of a hospital environment. Additionally, the data on acetaminophen use was restricted to what was recorded by the hospital, meaning any doses given by parents at home after discharge were not captured.
Finally, the parent-reported behavioral questionnaires are validated screening tools that help identify children at risk for autism, but they are not formal diagnostic instruments themselves. And though the study included a large number of children from multiple sites across the United States, the sample does not perfectly represent the entire population of American male newborns.
“We observed no association between circumcision and autism in boys, but it remains important to evaluate the safety of common medical procedures,” McGrath said. She and her colleagues are now examining other possible explanations for the increase in autism diagnoses.
The study, “Neonatal Medical Male Circumcision and Child Autism Diagnosis,” was authored by Monica McGrath, Xiuhong Li, Lisa P. Jacobson, Bennett Leventhal, Judy L. Aschner, Brennan Baker, Karla Cardoso Garcia, Aisha S. Dickerson, Amy J. Elliott, Jody Ganiban, Amanda Goodrich, Daniel B. Horton, Melinda Jarnecke, Sarah Keim, Brian K. Lee, Courtney D. Lynch, Mark Klebanoff, Abdul-Manaf Mutaru, Ruby H. N. Nguyen, Rebecca J. Schmidt, Hyeong-Moo Shin, Lauren C. Shuffrey, Jonathan L. Slaughter, Annemarie Stroustrup, Zhaozhong Zhu, Aaron A. R. Tobian, and M. Kate Grabowski.