Autism spectrum disorder (ASD) is characterized by impaired social communication and poor adaptation to change; thus, the onset of puberty may be a pivotal transition. This cross‐sectional study measured pubertal timing to examine hypothesized differences for sex (female vs. male) and group (ASD vs. typical development [TD]). Participants included 239 children (137 ASD, 102 TD) between 10 and 13 years. The ASD group included 35 females and 102 males; the TDs included 44 females and 58 males. Pubertal onset measured by genital or pubic stage was investigated with linear regression using main effects of sex and age‐by‐sex interactions in TD and ASD groups and main effects of diagnosis and diagnosis‐by‐age interactions in males and females, controlling for body mass index, socioeconomic status, and race. In TD, examination of main effects for genital (penis/breast) stage showed no difference for male and female children (t = 1.33, P = 0.187, rdf = 92); however, there were significant differences in ASD (t = 2.70, P = 0.008, rdf = 121). For diagnosis modeled separately by sex, there was significantly earlier pubertal development in females with ASD (t = 1.97, P = 0.053, rdf = 70, but not males (t = 1.329, P = 0.186, rdf = 143). In addition, analysis of menses revealed females with ASD had significantly earlier onset than TD (t = −2.56, P = 0.018, rdf = 21). Examination of pubic stage revealed expected sex differences for TD (t = 2,674, P = 0.009, rdf = 91) and ASD (t = 3.482, P = 0.001, rdf = 121). Females with ASD evidence advanced pubertal onset relative to ASD males and TD females. Findings underscore the need for enhanced understanding of pubertal development in ASD, as differences may have significant psychological, social, physiological, and developmental consequences.Lay SummaryChildren with autism spectrum disorder (ASD) have difficulty with social communication and respond poorly to change, which may include the onset and course of puberty. The study measured the timing of puberty in 239 children (137 ASD and 102 typical development [TD]) between 10 and 13 years based on pubertal stage of genital (breast/penis) and pubic hair development. Females with ASD evidence advanced pubertal onset relative to ASD males and TD females. Findings underscore the need for an enhanced understanding of pubertal development in ASD.