Fluoxetine hydrochloride is the first selective serotonin uptake inhibitor introduced commercially in the United States. This report describes preliminary clinical experience with fluoxetine in 10 children and adolescents, aged 8 to 15 years, with primary obsessive compulsive disorder (OCD) or Tourette's syndrome (TS) plus OCD. In general, fluoxetine, which was administered from 4 to 20 weeks at a dosage of 10 or 40 mg per day, was well tolerated. Adverse effects included behavioral agitation/activation in four patients and mild gastrointestinal symptoms in two patients. No abnormalities were noted in the seven children who had follow-up EKGs. Five of the 10 patients (50%) were considered responders; their obsessive-compulsive symptoms decreased substantially during treatment with fluoxetine. Responder rates were similar in the primary OCD (two of four, 50%) and TS + OCD (three of six, 50%) groups. In conclusion, short-term fluoxetine administration appears to be safe in children and adolescents. Placebo-controlled trials are needed to further assess the efficacy of fluoxetine.