PIP: There is striking evidence that there is an increased risk of early cancer mortality in women treated with diethylstilbestrol during pregnancy. Exposure to the drug is associated with more than a twofold increase in risk of all cancer, which increases to 2.89 for breast cancer, and to 2.73 for endocrine related tumors. Most published studies on the subject lack the statistical power to reject the hypothesis that there are no significant differences between treated and untreated women, especially in the presence of a 50% increase in risk. There is a difference in the magnitude of the relative risk between premenopausal and postmenopausal breast cancer, the mortality cases being primarily in premenopausal women. Additional studies on diethylstilbestrol are needed.