Bulimia nervosa (BN) is one of the most frequently encountered eating disorders in industrialized societies. It has been suggested that reduced serotonin activity may trigger some of the cognitive and mood disturbances associated with BN. Thus, pharmacologic treatment of BN is mainly based on the use of selective serotonin reuptake inhibitors, which have proved effective. At present, the biological basis of this disorder is not completely clear. The aim of this randomized, controlled trial was to verify the efficacy of sertraline, a selective serotonin reuptake inhibitor, in a group of patients with a diagnosis of BN. Twenty female outpatients, with an age range of 24 to 36 years and a diagnosis of purging type BN as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM IV), were assigned randomly to two treatment groups. The first group received sertraline 100 mg/day for 12 weeks; the second group received placebo. The study was conducted for 12 weeks, with weekly clinical assessments. At the end of the observation period, the group treated with sertraline had a statistically significant reduction in the number of binge eating crises and purging compared with the group who received placebo. In no case was treatment interrupted because of side effects. This study confirms that sertraline is well tolerated and effective in reducing binge-eating crises and purging in patients with BN.