It is estimated that 2 to 9 percent of women suffer from premenstrual dysphoric disorder (PMDD). Despite decades of research, effective treatments for the condition have eluded investigators. Research criteria for (PMDD) were established to promote investigation into the treatment and psychobiology of severe, dysphoric premenstrual symptomatology. Application of these new criteria to clinical trials adds needed rigor to research in this area and justifies the identification of effective treatments. In this study, rigorous criteria were utilized in a 12-center trial investigating the efficacy of the serotonin reuptake inhibitor sertraline in the treatment of PMDD. The study was completed and data was available for 162 women. A preliminary analysis demonstrated a positive response (very much improved or much improved) in 68 percent of patients treated with sertraline, compared with only 40 percent of patients treated with placebo (p < .01). This preliminary analysis provides strong support for the efficacy of sertraline as a treatment of severe premenstrual dysphoria.