A critical review of factors considered to cause menstrual dysfunction is women athletes with no overt organic cause for the abnormality is presented. Evidence suggests that although regular exercise can produce a specific change in hypothalamic-pituitary function, in particular reduced pulsatile luteinising hormone secretion, this is not associated with amenorrhoea or oligomenorrhoea in the majority of female athletes, most of whom continue to menstruate cyclically. Thus additional factors must be operative. It seems probable that severe menstrual dysfunction occurs in a specific predisposed subset of women athletes who have a particular personality type or body build and are attracted to a lifestyle including regular vigorous exercise. The biochemical basis may be related to hypothalamic, pituitary or even ovarian dysfunction possibly due to elevated levels of anti-reproductive hormones, including beta-endorphins, dopamine, prolactin and catechol oestrogens, induced by exercise; dopamine appears the most likely candidate. Chronic hypo-oestrogenic or eu-oestrogenic amenorrhoea or oligomenorrhoea may not be benign and should probably be treated in order to reduce the risk of osteoporosis or endometrial hyperplasia and adenocarcinoma.