Modification of the lateral closing wedge osteotomy of the proximal tibia is described for gonarthrosis associated with varus deformities. In this procedure, the anterior and posterior cortices are left attached to the distal and proximal fragments respectively when the bone wedge is removed. The defect is closed by applying valgus stress and medial rotation to the distal fragment so that the tibial tubercle advances anteriorly and the posterior cortex of the proximal fragment overrides the distal fragment. Contact area and stability at the osteotomy site are increased by an interlocking effect of the cortices and the stress under the patella is reduced by anterior advancement of the tibial tubercle. Satisfactory results have been obtained in 36 cases followed for one to three years with few complications.