In a large family with 37 members with multiple exostoses, only one person has developed sarcomatous degeneration of a lesion. Our review of published reports revealed great variation in the incidence of malignancy in multiple exostoses (10 to 25%). Most studies had sampling errors leading to the apparent overstatement of risk. In large pedigrees with essentially complete ascertainment of affected subjects, the risk of malignancy is nearer 3% or less. This lower risk for malignancy may be more appropriate in counselling affected subjects.