The association between spontaneous abortion and gestational trophoblastic disease (GTD) has been investigated in a study based on 93 women with 2 consecutive (repeated) spontaneous abortions and 82 control subjects who delivered normal babies. Nine molar pregnancies were observed among 7 of the 93 cases of repeated abortion while no control reported previous GTD. This difference was statistically significant and was not explained by allowance for age and number of pregnancies between cases and controls (chi 2(1) = 4.20; P = 0.04). When the observed number (9) of hydatidiform mole in the 385 pregnancies of the women with repeated abortion was compared with the expected one (0.28) based on the regional frequency data, the estimated relative risk was 32.1 with a 95% confidence interval from 13.9 to 63.3. The present findings confirm the association between GTD and spontaneous abortion and indicate that the risk is larger in women with repeated abortions.