The reproductive capability and labor complications of 98 women exposed to diethylstilbestrol (DES) in utero were compared with those of 3 separate control groups. The controls consisted of 167 age-matched, normal women, 20 siblings not exposed to DES who had achieved pregnancy, and their mothers. Spontaneous abortion, ectopic pregnancy, incompetent cervix, and premature labor occurred significantly more often in the DES-exposed population than in the normal controls. The controls also achieved a higher percentage of desired pregnancies overall; this was statistically significant (89.6 versus 75.0%, P<.001). When compared with their mothers, however, the DES-exposed population achieved a greater percentage of desired, viable pregnancies (75.6 versus 67.0%, P<.001). The unexposed siblings of the DES women achieved a higher percentage of desired, viable pregnancies than did their exposed sisters (86.9 versus 73.6%, P=.274), but less than the normal population (86.9 versus 89.6%).