This study analyses the prevalence of ASD, comorbidity, educational provision and ability in autistic children in a single health district, born between 1983 and 1996. The number of recorded diagnoses doubled over a 4 year period. This appeared to be due to greater recognition of ASD in more able children, in children initially presenting with ADHD, and possibly in females. ADHD accounted for a substantial proportion of comorbidity. Age at diagnosis appeared to be related to school placement. Cognitive ability levels ranging from more than three standard deviations below the mean to more than one standard deviation above the mean were found in the moderate and severe learning difficulty school population as well as in the mainstream population. Exceptionally low levels of verbal ability were present in a high proportion of mainstream pupils. Measured levels of cognitive function show poor relationship with actual educational placement.