Autism sex differences may be illusory
What if the long-discussed sex difference in autism is a function of age at diagnosis?
Publishing in the BMJ (the British Medical Journal) on 4 February 2026, an international group of researchers reported that a prospective, longitudinal study of births in Sweden over 35 years time revealed that about 2.8% of children were diagnosed as having autism, (b) the incidence of autism increased about every five years, and (c) the ratio of male-to-female diagnoses of autism became more equal as the children aged into adolescence. By adulthood, the ratio of males and females apparently is nearly even. The researchers explained that their findings indicate that the disproportionate ratio of males with autism may be a function of earlier diagnosis for boys.
The study, which was reported by Caroline Fyfe and colleagues (2026), is quite strong. The researchers studied all 2,756, 779 live births—not just a sample, but the entire population of births—for a long time. Because of the way that Sweden keeps medical records, they were able to ascertain which children were diagnosed as having autism at what age.
Fyfe et al. (2026) situated their findings in previous literature about male-female ratios. They noted an earlier meta-analysis by Loomes et al. (2017) showed higher incidence in boys than girls, but Fyfe et al. explained that only one of the 54 studies in the Loomes et al. data set had data spanning changes in diagnosis over such a long age span.
As Dear Readers who know a bit about autism likely would expect, a finding such as reported by Fyfe et al (2026) will merit broad news coverage. One of the best that I found is from the US public broadcasting news show, Science Friday. Flora Lichtman covered the Fyfe et al. study in a program 20 February 2026. A Web page on the Sci Fri site was devoted to the segment on autism rates among males and females; the segment not only has an interview with Professor Fyfe, but also additional content. Dear Readers may listen to an audio file (about 18 min long) as well as read a transcript.
There have been reports in sources such as Forbes (“Autism In Women May Be As Common As In Men, Study Finds”), Science Alert (“Autism Probably Affects Boys And Girls Equally, Massive New Study Reveals”), and the News International (“Shocking gender link in autism comes to light: New study has revealed a gender ratio of autism”).
References
Fyfe, C., Winell, H., Dougherty, J., Gutmann, D. H., Kolevzon, A., Marrus, N., Tedroff, K., Tunere, T. N., Weiss, L. A., Yip, B. H. K., Yin, W., & Sandin, S. (2026). Time trends in the male to female ratio for autism incidence: Population based, prospectively collected, birth cohort study. BMJ, 392, e084164. https://doi.org/10.1136/bmj-2025-084164
Loomes, R., Hull, L., & Mandy, W. P. L. (2017). What is the male-to-female ratio in autism spectrum disorder? A systematic review and meta-analysis. Journal of the American Academy of Child & Adolescent Psychiatry, 56(6), 466-474.