Enchondroma is a benign growth of cartilage arising in the bone metaphysis as a solitary or multiple primary lesions. The form of multiple enchondromatosis with unilateral predominance is termed Ollier's disease. We have recently treated a case of Ollier's disease with the chief complaint of deformity of the left hand. The patient was an 11-year-old boy. Radiographic examination showed honeycombed clear spaces in the metaphyses of the middle and proximal phalanges of the left ring and little fingers as well as of the fourth and fifth metacarpals, and thinning of the cortex of these bones, but with no evidence of pathological fracture. The tumors of the left fourth and fifth metacarpal bones and of the phalanges of the left ring and little fingers were removed, and the metacarpophalangeal joint of the little finger was capsulotomized. The patient was free from recurrence 19 months after surgery. With regard to the prognosis of Ollier's disease, malignant transformation into chondrosarcoma or osteosarcoma has been reported of the chondroma. Since Ollier's disease is self-limited in that it usually stops spontaneously as the patient grows, and since the cartilaginous lesions in occasional cases may regress or even disappear, any cartilaginous lesions that are still active or painful after termination of the growth period should be examined thoroughly under suspicion of undergoing malignant transformation.