The objective of this study was to evaluate the efficacy of fluvoxamine in the treatment of pathological gambling. Thirty-two patients were treated for 6 months in a double-blind, placebo-controlled study of fluvoxamine 200 mg/day. Outcome measures included reduction in money and time spent gambling per week. Longitudinal mixed effects models and completers analyses were used for estimation and hypothesis testing. Fluvoxamine was not statistically significantly different from placebo in the overall sample. However, fluvoxamine was statistically significantly superior to placebo in males and in younger patients. The power of the study was limited by the high (59%) placebo-response rate. Fluvoxamine may be a useful treatment for certain subgroups of patients with pathological gambling. Several methodological recommendations are made for future pharmacological trials of pathological gambling.