Self-injurious ideation or behavior appeared de novo or intensified during fluoxetine treatment of obsessive-compulsive disorder in six patients, age 10 to 17 years old, who were among 42 young patients receiving fluoxetine for obsessive-compulsive disorder at a university clinical research center. These symptoms required the hospitalization of four patients. Before receiving fluoxetine, four patients had major risk factors for self-destructive behavior including depression or prior suicidal ideation or self-injury. Three hypotheses concerning the apparent association between fluoxetine and these self-injurious phenomena are discussed: (1) coincidence; (2) disorganization of vulnerable individuals secondary to drug-induced activation; and (3) a specific serotonergic-mediated effect on the regulation of aggression.