Background: Few studies have examined the impact of gender, age at onset, phenotype and comorbidity in pediatric obsessive-compulsive disorder (OCD) in children. In this naturalistic study we consider these characteristics of OCD in the framework of the 4 OCD phenotypes (contamination/cleaning, order/symmetry, obsessions/checking and hoarding) proposed by Leckman et al. Sampling and Methods: A consecutive series of 257 patients aged 13.6 ± 2.8 years, diagnosed using a DSM-IV-based clinical interview (Schedule for Affective Disorders and Schizophrenia for School Age Children – Present and Lifetime Version), were included. Results: Patients with OCD onset before 12 years of age presented a higher frequency of comorbid tic disorder and disruptive behavior disorders. The type of obsession varied with gender: order/symmetry was more frequent in males, contamination/cleaning in females. Order/symmetry had the highest comorbidity with tics, contamination/cleaning was the least severe according to the Clinical Global Impression Severity, and was associated with a high rate of comorbid anxiety and depression, similarly to sexual-religious obsessions. Hoarding was the severest according to the Clinical Global Impression Severity, and was associated with a high comorbidity with social phobia and bipolar disorder. Tic comorbidity was more prevalent in males, had an earlier onset, and a heavier comorbidity with attention deficit hyperactivity disorder and other disruptive behavior disorders. A comorbid attention deficit hyperactivity disorder was associated with an earlier onset of OCD and a poorer response to treatments. Conclusions: OCD phenotypes and comorbidities may have marked clinical and prognostic implications. Tertiary care population results may not generalize to less impaired juvenile populations.