The premenstrual syndrome is a complex of physical and psychological symptoms of unknown aetiology, not associated with organic disease, which recur regularly during the same phase of each ovarian cycle and then regress. Ovulation but not menstruation is essential to the diagnosis. The type of symptoms (physical, e.g., oedema, weight gain, bloating and breast tenderness, and psychological, e.g., irritability, tiredness, depression), but not their severity remain constant from one cycle to the next. The diagnosis is usually based on history and self-assessment questionnaires. The prevalence ranges from 20% to 40% of the population.