In the present study, we have investigated the influence of comorbid attention deficit hyperactivity disorder (ADHD) on early onset obsessive compulsive disorder (OCD). For that purpose, we compared 20 patients with "OCD with ADHD" and 20 randomly selected patients with "OCD without ADHD". "OCD with ADHD" patients tended to show an earlier age of OCD onset, a higher severity of symptoms and a higher persistence rate than OCD patients without ADHD. Both groups appear to develop different patterns of comorbid disorders.