Approximately 8-10% of premenopausal women experience moderate to severe perimenstrual breast pain or cyclical mastalgia, monthly. This mastalgia can occur regularly for years until menopause, can interfere with usual activities, and is associated with elevated utilization of mammography among young women. Although mastalgia is a well documented symptom in premenstrual syndrome (PMS), it is unknown whether PMS is necessarily present in women with cyclical mastalgia. The present study prospectively examined mastalgia and its relationship to PMS. Thirty-two premenopausal women reporting recent mastalgia completed breast pain and menstrual symptom scales daily for 3-6 months. Eleven women (34.4%) met criteria for clinically significant cyclical mastalgia, reporting an average of 10.2 days of moderate-severe mastalgia monthly. Five women (15.6%) met criteria for PMS. Mastalgia was not significantly associated with PMS: 82% of women with clinical cyclical mastalgia did not have PMS. Cyclical mastalgia, although by definition associated with the menstrual cycle, is not simply premenstrual syndrome, and merits further investigation as a recurrent pain disorder whose presentation, etiology, and effective treatment are likely to differ from those of PMS.