This article reports on gender ratio, age of diagnosis and the duration of assessment procedures in autism spectrum disorder diagnosis in a national study which included all types of clinical services for children and adults. Findings are reported from a retrospective case note analysis undertaken with a representative sample of 150 Scottish children and adults recently diagnosed with autism spectrum disorder. The study reports key findings that the gender ratio in this consecutively referred cohort is lower than anticipated in some age groups and reduces with increasing age. The gender ratio in children, together with the significant difference in the mean age of referral and diagnosis for girls compared to boys, adds evidence of delayed recognition of autism spectrum disorder in younger girls. There was no significant difference in duration of assessment for males and females suggesting that delays in diagnosis of females occur prior to referral for assessment. Implications for practice and research are considered.