We reviewed the clinical and radiographic results of varus osteotomy of the proximal aspect of the femur and transfer of the adductor and external oblique muscles (the McKay procedure) in thirty-four children (sixty-six hips) who had an unstable hip secondary to a myelomeningocele at the middle or caudad lumbar level. The average age at the time of the operation was twenty months (range, seven to forty-two months). The average duration of follow-up was 10.9 years (range, 0.7 to 20.0 years). An open reduction was performed in ten hips. None of the children had had any previous operative treatment.The index operation helped to maintain the stability of thirty-seven of the fifty-one hips in twenty-six children who remained neurologically stable: seventeen of nineteen hips that were at risk, two of three hips with acetabular dysplasia, fifteen of sixteen subluxated hips, one of three dislocated hips that had been previously reduced with a Pavlik harness, one of two dislocatable hips, and one of seven previously untreated dislocated hips. The index operation was not successful for one dislocated hip that had been treated with closed reduction and application of a spica cast. The operation was a success for eight of the fifteen hips in eight children who had a progressive loss of neurological function: three of five hips that were at risk, one hip with acetabular dysplasia, two of four subluxated hips, one of two hips that had been previously reduced with a Pavlik harness, and one dislocatable hip. Two dislocated hips redislocated.Initially the index operation was performed on all children who had a myelomeningocele at the third or fourth lumbar level. Recent data have shown that the hips in these children are not all at risk, and we now perform the operation only if there is documented instability of the hip.