To examine differences by sex in the timing of identification of individuals with autism spectrum disorders (ASD), survey data were collected in the Netherlands from 2,275 males and females with autistic disorder, Asperger’s syndrome and PDD-NOS. Among participants <18 years of age, females with Asperger’s syndrome were identified later than males. Among participants ≥18 years of age, females with autistic disorder were identified later than males. In more recent years, girls with Asperger’s syndrome are diagnosed later than boys, confirming earlier findings. In adults, the delayed timing of diagnosis in females with autistic disorder may be related to changing practices in diagnosis over time. Strategies for changing clinician behaviour to improve recognition of ASD in females are needed.