Hereditary multiple exostosis (HME), a bone tumor first described by Virchow, has been studied over a period of 15 years on a comparative basis. The horse, an excellent biomedical model for this physically deforming multiple bone tumor in man, has been utilized in this study. The etiology, hereditary pattern, potential for malignancy and other aspects of this strange affliction need additional clarification. This in-depth study of 261 individuals from 144 families was compared with that of 55 horses bearing the HME trait, selectively bred and studied over the same period. Important information has been collected and evaluated about this condition that is suspect of being frequently missed diagnostically, with a higher incidence in humans that recognized. Continuing development studies of offspring of the original study participants; sarcomatous transformation monitoring; and recently developed genetic techniques should add to our understanding of this puzzling hereditary condition.