Background: Previous studies have reported variable and at times opposite findings on comorbid psychiatric problems in children with autistic spectrum disorders (ASD). Aims: This study aimed to examine patterns of comorbid psychiatric problems in children with ASD and their parents compared with IQ matched controls and their parents. Methods: Behavioural/emotional problems were evaluated in a sample of children with ASD [a diagnosis of ASD was given if they met criteria for ASD on both of the ADI-R (Autism Diagnostic Interview-Revised) and ADOS (Autism Diagnostic Observational Schedule)] and an age and IQ matched control group using the Child Behavior Checklist (CBCL/6-18). Parental psychological distress for both groups was evaluated with the Brief Symptom Inventory (BSI). Results: There were 59 (88%) boys and 8 (12%) girls in the ASD group. Similarly, 57 (85%) of the control group were male and 10 (15%) were female. The groups did not differ significantly on mean age, mean IQ scores, gender and parents mean age. Results of the CBCL/6-18 revealed that the majority of parents reported their child with ASD as having either internalising (clinical range: 47.8%; borderline range: 16.4%) or externalising problems (clinical range: 10.4%; borderline range: 20.9%). In the control group more parents reported their children having externalising (clinical range: 46.3%; borderline range: 16.4%) than internalising problems (clinical range: 35.8%; borderline range: 11.9%). Almost a half of the ASD group met CBCL DSM criteria for clinically significant attention deficit hyperactivity disorder (44.78%) and anxiety (46.2%) problems. Based on the Brief Symptom Inventory Global Severity Index 22.4% of fathers and 23.8% of mothers of ASD children produced scores that were indicative of possible psychopathology. Conclusions: High rates of clinically significant psychiatric problems were detected in ASD children, with anxiety and attention deficit hyperactivity disorder being the most frequently detected syndromes.