Obsessive-compulsive disorder affects approximately 2% of the population, frequently has its onset during childhood or adolescence and is potentially incapacitating. If not properly treated, this disorder tends to follow a chronic course. Pharmacotherapy with clomipramine and selective serotonin reuptake inhibitors (SSRIs), such as fluvoxamine, fluoxetine and sertraline, has been approved for pediatric OCD. However, up to 30% of patients may not benefit from these treatments, and the presence of residual symptoms is frequent among treatment responders. Cognitive-behavioral therapy (CBT) is also recognized as first line treatment for pediatric OCD, either administered in individual or group format. There is evidence suggesting equivalent efficacy for SSRIs and CBT in pediatric OCD, but there is no data on adaptive treatment strategies regarding such treatments on the long term outcome of OCD patients. The aim of this study is to verify, in a randomized design, if there is an optimal sequential treatment strategy for pediatric OCD, adopting the two most studied treatments for this disorder: an SSRI and group CBT (GCBT). The investigators hypotheses are: (1) both types of treatment will present similar efficacy in the short term (14 weeks); (2) for non-responders to the first type of treatment (fluoxetine up to 80mg/day or GCBT for 14 weeks), combined treatment (fluoxetine + GCBT for another 14 weeks) will be more effective than switching treatment modality (from fluoxetine to GCBT or from GCBT to fluoxetine for additional 14 weeks) after additional 14 weeks.

This is a 28-week open protocol, composed of two phases of randomized treatments with 14 weeks duration.

Inclusion criteria: DSM-IV diagnosis of OCD; age between 7 and 17 years; willing to participate in the protocol; parents or legal tutors agreement with their child participation in the protocol; absence of physical or cognitive impairment that prevent the participation in the protocol.

We expect to end the protocol with 50 patients in each arm (total = 200). For this reason, the purpose is to recruit at least 400 patients for the first randomization (R1: fluoxetine X group CBT). Responders to the initial type of treatment will be maintained in the same procedure for additional 14 weeks. The second randomization (R2) will address non-responders to fluoxetine, who will be randomized to switch to group CBT or receive group CBT as add-on therapy; and non-responders to group CBT, who will be randomized to switch to fluoxetine or receive fluoxetine as add-on therapy.

Fluoxetine will be administered in drops or capsules, in doses ranging from 10 to 80mg/day. Group CBT will be delivered weekly, in 2-hour sessions, in groups of 6 to 8 participants.

At the end of each treatment (weeks 14 and 28), treatment response will be assessed by blind raters, through the YBOCS and CGI-global improvement subscale. Response will be defined as at least 35% reduction in baseline YBOCS scores and a CGI score of 1 or 2.

Efficacy of treatments at the end of R1 will be compared and the efficacy of the different sequences of treatments at the end of R2 (adaptive treatment strategies) will be compared by means of an intention-to-treat analysis.

Inclusion Criteria:

• diagnosis of obsessive-compulsive disorder according to DSM-IV as major problem
• 7 to 17 years
• who agree to participate in the research
• who have parental permission or legal guardian to participate in the research
• that do not have physical or cognitive impairments that prevent the participation of research
• YBOCS ≥ 16 for obsession and compulsion or ≥ 10 for only obsession or compulsion only
• Be above the tenth percentile of weight corresponding to age
• IQ greater than 80 - assessed using the Raven (the screening, if necessary)

Exclusion Criteria:

• Inability to study evaluated adherence to the beginning.
• ANY medical or neurological condition that determines contraindication to any of the treatments or that may influence the evaluation protocol
• pregnancy (women of childbearing age should use contraception)
• Suicidal ideation (with intent) CURRENT