Summary The prevalence (lifetime occurrence) rate of cancers of the reproductive system (uterus, ovary, cervix and vagina) and breast cancer was determined for 5,398 living alumnae, 2,622 of whom were former college athletes and 2,776 non-athletes, from data on medical and reproductive history, athletic training and diet. The former athletes had a significantly lower risk of cancer of the breast and reproductive system than did the non-athletes. The relative risk (RR), non-athletes/athletes, for cancers of the reproductive system was 2.53. 95% confidence limits (CL) (1.17, 5.47 This study was suggested by the findings that strenuous exercise delays menarche (Frisch et al., 1980;Warren, 1980;Frisch et al., 1981) and that women dancers and athletes, including college athletes, have a high incidence of oligomenorrhoea and secondary amenorrhoca (Frisch et al., 1981;Dale et al., 1979;Frisch et al., 1980