Forty-seven women (29 with unexplained infertility and 18 with menstrual dysfunction) practiced weight control by caloric restriction in order to maintain a fashionable body habitus. All of these women were below ideal body weight (IBW) when compared with Metropolitan Life Insurance Company tables for height and weight. When 36 of these women followed a dietary regimen designed to increase their weight to predicted IBW, 19 of 26 infertile women (73%) conceived spontaneously; 9 of 10 women (90%) with secondary amenorrhea resumed menstruation. Eleven women (23%) would not accept their practice of weight control as the cause of reproductive failure and did not participate in the study. Differences in the serum gonadotropin luteinizing hormone:follicle-stimulating hormone (LH:FSH) ratio were found to be significantly related to differences in the percentage of IBW. The practice of weight control may be a cause of unexplained infertility and menstrual disorders in otherwise healthy women.