Premenstrual syndrome (PMS) is a group of psychological and physical symptoms which regularly occur during the luteal phase of the menstrual cycle and resolve by the end of menstruation. The severe and predominantly psychological form of PMS is called premenstrual dysphoric disorder (PMDD). The exact aetiology of PMS is not known. PMS results from ovulation and appears to be caused by the progesterone produced following ovulation in women who have enhanced sensitivity to this progesterone. The increased sensitivity may be due to neurotransmitter (mainly serotonin) dysfunction. The key diagnostic feature is that the symptoms must be absent in the time between the end of menstruation and ovulation. Prospective symptom rating charts are used for this purpose. Treatment is achieved by suppression of ovulation or reducing progesterone sensitivity with selective serotonin re-uptake inhibitors. In this chapter, the authors describe the aetiology, symptoms, diagnosis and evidence-based management of premenstrual syndrome.