Enchondromatosis or OLLIER's disease or multiple chondromatosis can be marked in his development by features like: malignant degeneration, pathological fracture, deformity or shortening of a limb. The limb deformity like a varus knee was for our two little patients their admission motive. The varus gravity (equal to 30%) was treated by a early tibial valgus osteotomy in one case and a femoral one in the other case. We evocate the unusualness of this disease, the clinical diagnostic difficulties composed by the knee varus in childhood, at the radiographic stage those of a benignant metaphysis or metaphyso-diaphysis tumor in the same year old. We discuss the osteotomy moment, its type, its site and expose the concomitant problems composed by the shortening of the limb.