Objective – To evaluate potential differences in socio-demographic and clinical characteristics (obsessivecompulsive symptomatology, axis I and II comorbidity) between OCD adults with an early age at onset (≤18 years) and later onset, (≤18 yrs). Design – Clinical controlled study. Setting – Anxiety and Mood Disorders Unit, Department of Neuroscience, University of Turin. Methods – We included 149 subjects with a principal diagnosis of OCD (DSM-IV) and a Y-BOCS total score ≤ 16 All patients underwent a semistructured clinical interview aimed at investigating sociodemographic characteristics and clinical features of the disorder. Lifetime Axis I comorbidity, according to DSM-IV criteria, was investigated with a structured interview following Othmer & Othmer guidelines (1994; 1999). Personality disorders were assessed using the Structured Clinical Interview for DSM-IV Axis II Disorders (SCID-II). Results – 39 patients referred age at onset of OCD before 18 years (earlyonset group) and 110 patients at 18 years or later (later-onset group). Significant differences were found between the two groups: early-onset subjects are characterized by a preponderance of males, a chronic course of illness and a strong association with Schizotypal Personality Disorder. Discussion – When subtyping OCD according to age at onset we found significant differences which suggest a possible heterogeneity of the disorder. Our results seem to confirm that early-onset OCD may represent a more severe subgroup, with clinical characteristics such as the chronic course and the high association with Schizotypal PD which are significant in order to apply specific therapeutic strategies.