Excessive Siamese twinning in Southern Africa.

Twelve sets of conjoined twins have been born in Southern Africa since February 1974. This possibly represents a significant increase in the incidence of Siamese twinning and may be the result of unknown environmental agents. Several of the sets of twins were diagnosed antenatally. In view of the current circumstances a high index of suspicion is probably justified in the presence of maternal hydramnios or fetal malpresentation.