A Caucasian family is presented in which two out of three children showed lesions resembling gigantiform cementoma clinically, radiologically and histopathologically. Both affected children had swellings of the alveolar crest, caused by large, lobular, radio-opaque masses in all four quadrants of the jaws. Histologically, cementum-like masses were surrounded by inflamed fibrous connective tissue. There was evidence indicating that the late father had similar lesions which became malignant following radiation therapy.