Premenstrual disorders are characterized by numerous mood, somatic and behavioral symptoms that occur during the late luteal phase of a woman's menstrual cycle and abate soon after the onset of menses. Diagnostic criteria for premenstrual syndrome (PMS) were published by the American College of Obstetricians and Gynecologists in 2000; the American Psychiatric Association had previously established very specific diagnostic criteria for premenstrual dysphoric disorder (PMDD). Both diagnoses require 2 months of prospective symptom ratings, which can be accomplished using forms designed by individual clinicians or employing 1 of a number of validated instruments. The patient will need to provide a complete family and personal history of mental disorders and medical diseases. A thorough physical examination and certain basic laboratory tests should either identify or rule out many potential causes of the symptoms. The diseases, disorders or situations considered in the differential diagnosis of PMS and PMDD will depend on the woman's presenting symptoms. Many women with a bothersome or debilitating premenstrual disorder go undiagnosed, either because they do not report their symptoms to a clinician or because the clinician has difficulty diagnosing the disorder.