Prevalence of current comorbid DSM-IV disorders was assessed in a special school population of children and adolescents with ASD (N = 71, age 6.0-17.9 years), representing all cognitive levels and main ASD subgroups. Symptoms were assessed through parent interview and association to child characteristics was explored. Seventy-two percent was diagnosed with at least one comorbid disorder. Anxiety disorders (41%) and attention deficit/hyperactivity disorder (31%) were most prevalent. Obsessive-compulsive disorder was more common in older children, and oppositional defiant disorder/conduct disorder more prevalent in pervasive developmental disorder, not otherwise specified. Our results show high rates of comorbid DSM-IV disorders and underscore the importance of such evaluation in children ASD. However, diagnostic challenges are present and future research on the diagnostic validity of comorbid psychiatric disorders is needed.