Objective: This systematic review summarizes the evidence from randomized clinical trials of bright light therapy for treatment of premenstrual dysphoric disorder. Study design: The authors performed a systematic review and meta-analysis of randomized clinical trials. They searched MEDLINE, AMED, CINAHL, Digital Dissertations, EMBASE, and the Cochrane Central Register of Controlled Trials. The main outcome measure was the change in depressive symptom scores as measured by the Hamilton Depression Rating Scale and the Beck Depression Inventory. Results: Four crossover trials studying a total of 55 participants met inclusion criteria. Three trials showed similar results; one fully unblinded trial showed a much larger effect. The pooled effect size from the random-effects model of the 3 higher quality trials was -0.20 (95% CI -0.48 to 0.07). Conclusion: The small size of trials and correspondingly wide confidence limits, and methodologic limitations of the trials, leaves the impact of bright light therapy for relief of premenstrual depressive symptoms uncertain. The current evidence justifies neither enthusiastic dissemination nor confident rejection of this therapeutic modality. © 2005 Mosby, Inc. All rights reserved.