A retrospective review of twenty-one patients with Ollier's disease showed that the lesion involved the femur and tibia most frequently, and that those bones accounted for the large majority of clinical problems. Angular deformities were common; 80 per cent of the affected femora had clinically significant varus or valgus angulation in the distal part and 42 per cent of the affected tibiae had proximal or distal deformity. The apex of the angulation, when present, was metaphyseal, with the concavity on the side that was more extensively involved by the enchondromas. Osteotomies were done frequently to correct angulation; all healed well. Deformity in the distal part of the femur frequently required repeat osteotomy to achieve a straight bone at skeletal maturity, The extent of shortening, which always was present in the involved limb, closely paralleled the extent of involvement, The discrepancies in limb lengths prior to surgical treatment averaged 9.8 centimeters (range, 4.3 to 35.7 centimeters). Epiphyseal arrest, when appropriately timed, was effective in correcting or limiting the discrepancies, but partial (medial or lateral) epiphyseal arrest to correct angular deformity was ineffective. Diaphyseal lengthening was done on six occasions, once in the femur and five times in the tibia and fibula, with good results. Fourteen pathological fractures occurred in seven of the twenty-one patients, and all healed uneventfully with conservative treatment.