Menstrual dysfunction characterized by delayed menarche, irregular menses, or secondary amenorrhea often affects women who compete in athletics over a prolonged time. Loss of body fat and emotional stress are important predisposing factors. Under these circumstances, hypoestrogenism, an altered ratio of follicle-stimulating hormone to luteinizing hormone, and elevation of serum testosterone, prolactin, catecholamines, and opioids are fairly common. There is controversy over whether the working capacity and performance of the average woman varies appreciably during various phases of the menstrual cycle. Apparently, those who suffer from premenstrual tension do have a diminution in working capacity. Generally, the causes of menstrual dysfunction are the same for athletes and nonathletes, and there are currently no data to forbid athletes' training at any time during the menses. A gynecologic examination should be done before menstrual dysfunction is considered to be due to physical exercise. If this assumption is substantiated, and if amenorrhea persists for one year or more, a periodic estrogen-progesterone regimen should be offered to minimize vascular problems, osteoporosis, and stress fractures, and to protect the endometrium and ovarian function.