A multicenter, double-blind, 12-week, placebo-controlled trial of 411 randomized patients, predominantly women diagnosed with posttraumatic stress disorder, failed to show a difference between either dose of fluoxetine treatment and placebo. The mean changes from baseline (SD) measured by the Clinician-Administered PTSD Scale scores were -42.9 (23.1), -42.8 (27.9), and -36.6 (25.7) in the 20-mg fluoxetine, 40-mg fluoxetine, and placebo arms, respectively. Placebo response rate was substantially higher in this study than in a previously published fluoxetine trial of posttraumatic stress disorder.