Recent reports indicate that proximal tibial osteotomy for osteoarthritis of the knee is contraindicated if subluxation of the joint is evident clinically or on weight-bearing X-rays, or if the angular deformity of the joint is greater than 15 degrees. The purpose of this paper is to present evidence that a proximal tibial osteotomy, properly planned and performed, can give consistently sat-sfactory results even in osteoarthritic knees which have preoperative varus deformities greater that 15 degrees or are subluxated. A proper planning requires an exact measurement of the deformity on full length X-rays, a precise preoperative drawing and a very exact osteotomy giving some overcorrection. The overcorrection must compensate for the weakness of the lateral muscles, the most frequent cause of the condition.