BACKGROUND Very little research has examined the frequency with which women with major depressive disorder experience premenstrual exacerbation (PME) of depression or the characteristics of those who report such worsening. The NIMH Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study provides a unique opportunity to evaluate PME in depressed women seeking treatment in primary care or psychiatric settings. METHODS This report presents data from the first 1500 participants enrolled in the STAR*D study. Premenopausal women with major depressive disorder were asked if they experienced a worsening of their depressive symptoms 5-10 days prior to menses. Those reporting PME were compared with those reporting no PME with regard to sociodemographic characteristics, course of illness features, symptom presentation, general medical co-morbidity, functional impairment, and quality of life. RESULTS Of 433 premenopausal women not taking oral contraceptives, 64% reported a premenstrual worsening of their depression. Women who reported PME had a longer duration of their current major depressive episode [30.7 (S.D. = 73.7) months versus 13.5 (S.D. = 13.2) months; p=0.001], as well as greater general medical co-morbidity. Women reporting PME were also more likely to endorse symptoms of leaden paralysis, somatic complaints, gastrointestinal complaints, and psychomotor slowing, and were less likely to endorse blunted mood reactivity. CONCLUSIONS PME is endorsed by the majority of premenopausal women with major depressive disorder and appears to be associated with a longer duration of depressive episode. PME is a common and important clinical issue deserving of further attention in both research and practice.