Premenstrual dysphoric disorder (PMDD), a menstruous dysfunction, is characterized by profoundly depressed mood, and studies have shown that antidepressants are effective for PMDD. The authors describe a case of PMDD who was initially treated with selective serotonin reuptake inhibitors. Due to intolerable gastrointestinal side effects with selective serotonin reuptake inhibitors, St. John's wort (900 mg/day) was substituted and much improvement in PMDD symptoms was noted for at least five-month follow-up. The authors propose that St. John's wort could be an alternative medication for PMDD, especially for patients experiencing intolerable side effects with selective serotonin reuptake inhibitors.