The objective of this study is to examine the occurrence and characteristic features of obsessive–compulsive behaviours in children and adolescents with Asperger syndrome (AS), with respect to a matched obsessive compulsive disorder group (OCD) and a typically developing control group (CG). For this purpose, 60 subjects (20 OCD; 18 AS; 22 CG), aged 8–15 years, matched for age, gender and IQ were compared. AS and OCD patients were diagnosed according to the DSM-IV-TR criteria. The Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule were used to assist in the AS diagnosis; the WISC-R was administered to assess IQ. Obsessive and compulsive symptoms were evaluated by using the Children’s Yale-Brown Obsessive-Compulsive Scale (CY-BOCS). None of the AS children received a formal diagnosis of OCD. The AS group presented significantly higher frequencies of Hoarding obsessions and Repeating, Ordering and Hoarding compulsions compared to CG. The OCD group, in turn, reported significantly higher frequencies of Contamination and Aggressive obsessions and Checking compulsions compared to both the AS group and CG. As expected, the OCD group displayed a higher severity of symptoms (Moderate level of severity) than did the AS group (Mild level of severity). Finally, in our sample, neither the OCD group nor the AS group demonstrated a completely full awareness of the intrusive, unreasonable and distressing nature of symptoms, and the level of insight did not differ between the OCD group and CG, although an absence of insight was observed in the AS group. Children with AS showed higher frequencies of obsessive and compulsive symptoms than did typically developing children, and these features seem to cluster around Hoarding behaviours. Additionally, different patterns of symptoms emerged between the OCD and AS groups. Finally, in our sample, the level of insight was poor in both the OCD and the AS children. Further research should be conducted to better understand the characteristics of repetitive thoughts and behaviours in autism spectrum disorders, and to clarify the underlying neurobiological basis of these symptoms.