The radiographic anatomy, functional status, and impairment ratings of twenty-eight patients (fifty-six extremities) who had hereditary multiple exostoses were evaluated. The patient (or the parent) also subjectively graded the function of each extremity with use of a standard rating-assessment tool. Degenerative joint disease was evident in three (5 per cent) of the fifty-six extremities at the time of follow-up, when the patients were an average of twenty-one years old. With use of the hand test of Jebsen et al., the average score was in the forty-seventh percentile for the dominant extremity and in the twenty-eighth percentile for the non-dominant extremity. Loss of pronation and supination increased with increasing age. Dislocation of the radial head was significantly associated with negative ulnar variance (p = 0.008) and with the impairment rating (p = 0.001), but not with the subjective score or with the performance on the hand test of Jebsen et al. So-called whole-person impairment ratings ranged from 0 to 17 per cent (average, 5 per cent). It has been our experience that deformities of the upper extremity in patients who have hereditary multiple exostoses are well tolerated and lead to little loss of function as measured both subjectively and objectively.