We have reviewed the results of 30 operations performed on 23 patients with Ficat stage-III or stage-IV osteonecrosis of the femoral head in which autogenous cortical and cancellous bone grafting had been performed through a so-called trapdoor made in the femoral head. At a mean of 56 months (30 to 60) after operation 20 of 24 stage-III hips (83%) had a good or excellent result as determined by the Harris hip-scoring system. Two of six stage-IV hips (33%) had good or excellent results. Eighteen of 21 hips (86%) with a combined necrotic angle of 200 degrees had good or excellent clinical results compared with only four of nine hips (44%) with a combined necrotic angle of more than 200 degrees. Six of the eight hips which had fair or poor results were in patients who had received corticosteroids; five of these six hips had lesions with a combined necrotic angle of greater than 200 degrees or were in a late stage (stage IV). There were no perioperative complications. Our results suggest that the trapdoor procedure with autogenous cancellous and cortical bone grafting can be successful in Ficat and Arlet stage-III osteonecrosis of the hip in patients with small- to medium-sized lesions.