There is an ongoing debate as to whether autism spectrum disorder (ASD) is expressed differently in women than men. It is unclear whether differences found are specific to autism or merely reflecting normative development. In this study, we compared sex differences in developmental trajectories of autistic and co-occurring psychopathological symptoms in adolescents with milder forms of autism to those in a normative group matched for intelligence quotient (IQ) and socioeconomic status. Data of five assessment waves from ages 11 to 22 years were analyzed using linear mixed modeling. We found that in adolescence, sex differences in developmental trajectories of psychopathological symptoms specific for autism are confined to the repetitive stereotyped domain (males had higher scores on the sensory/stereotypic and resistance to change domains, the latter difference disappeared during adolescence due to an increase of these problems in females with ASD). Other sex differences, among which an increase over time in affective and anxiety problems in females was the most outstanding, were also observed in typically developing females. These sex-specific differences have relevance in the clinical care of men and women with autism, although they are subtle compared to differences between individuals with and without autism, which are broadly present in internalizing and externalizing problem domains.