A prospective study was undertaken during an 18-month period with 64 families who had endothelial dystrophy. Two hundred twenty-eight relatives were examined. Of those older than the age of 40, 38% were affected. Women were affected more severely and 2.5 times more frequently than men. The disease showed a strong familial tendency: there was one family in which three generations were affected and 16 families in which two generations were affected. There were four families that had members with edema in two generations. There was no association between edema in a parent and edema in a child. The proportion of relatives affected and the severity of involvement increased with age. Fifty-three probands and 18 relatives had endothelial dystrophy with edema (Fuchs' dystrophy). Of these 71, one had glaucoma.