The authors discuss the anatomical, structural and biomechanical aspects of osteoarthrosis of the hip that are the determining factors in the success of varizing osteotomy, based on a pre-operative radiological and clinical study of their cases. In describing the surgical technique, they stress the importance of posterior capsulotomy. The case material comprises thirty-two patients, twenty-seven of whom underwent osteotomy. Five received no surgical treatment and two of those operated on had no pre-operative dysplasia. All patients were followed up roughly ten years after operation. The same criteria of assessment were used as those recorded at the time of operation and included pain, mobility, walking and radiological appearances. The results obtained confirm the effectiveness of varizing osteotomy with posterior capsulotomy, provided that it is preceded by a careful assessment of the patient to ensure that the correct indications have been observed.