Among 2,968 women and girls exposed to crocidolite (blue asbestos) at Wittenoom, three cases of choriocarcinoma and three cases of hydatidiform mole have been identified (crude incidence rate of 9.9 per 1000 women and 1.7 per 1000 deliveries for choriocarcinoma and hydatidiform mole, respectively). The women with choriocarcinoma were resident at Wittenoom at the time of disease development, whereas hydatidiform mole occurred much later in women who had first been exposed to asbestos as young girls. Four of the six cases were known to have lived with asbestos company workers who brought their dusty work-clothes home for washing. Asbestos fibers have been reported in the lung, the pleural and peritoneal mesothelium, and the human ovary. They have also been detected in placental digests of live and stillborn infants. This cluster of gestational trophoblastic diseases has some biological plausibility for asbestos causation. Taking an occupational and residential history and examining pathologic specimens for asbestos fibers or bodies may prove useful in patients with gestational trophoblastic disease.