Premenstrual syndrome: an update for the clinician. Premenstrual syndrome is a complex disorder in which a variety of symptoms can occur in the luteal phase of the menstrual cycle. The symptoms should occur each cycle only from the time near ovulation to soon after the onset of menses. There should be at least 1 week in follicular phase that is symptom-free. Symptoms should be severe enough to significantly interfere with the ability of the patient to function within her normal lifestyle. Diagnosis is based on clinical information from prospective charting of symptoms. Up to 50 per cent of patients who think they have PMS really suffer from another type of mental illness, usually a depressive disorder. Laboratory tests are not generally helpful in the diagnosis. Treatment is based on the type(s) of symptom(s). Available treatments are reviewed with documentation of results from double-blind placebo-controlled experimental designs. The etiology of PMS is not known. However, there are good empiric therapies available that can help most PMS patients. 