Sex differences have been found amongst toddlers and young children with autism spectrum disorder (ASD). We investigated the presence and stability of these ASD sex differences throughout childhood and adolescence. Participants (N = 325, 52 females; aged 3-18 years) consecutively received an ASD diagnosis at a clinic for assessing high-functioning ASD (mean verbal IQ = 92.6). There were no IQ sex differences. By parent report and direct observation, females had less repetitive stereotyped behaviour (RSB), with male-equivalent levels of social and communication impairment. Teachers reported males with ASD as having greater externalising and social problems than females. The female phenotype we describe was stable across our sample's age range. Their milder RSBs and less severe difficulties at school may lead to under-recognition of ASD in females.

Are children with an autism spectrum disorder (ASD), but normal-range intelligence, impaired on theory of mind skills measured by responses to abstract animations in the form of a computerized cartoon? Fifty-six cases and closely matched comparisons were tested. We rated verbal responses according to the length of their descriptions, their appropriateness and the children's use of 'mentalizing' terms. Children with ASD used 'mentalizing' language to describe the animations as well as comparisons, although the content of their descriptions was significantly less appropriate. Performance on this task was not well correlated with standardized measures of parent-reported behaviour or the child's interactions with an observer. The implications of our results are discussed in relation to previous studies that have used this methodology.