To elucidate the factors important for development of avascular necrosis of the femoral head following traumatic posterior dislocation of the hip, 98 adult patients with 100 hip dislocations were reviewed after a minimum follow-up of 5 years. Avascular necrosis of the femoral head was found in only 4.8% of the hips reduced within 6 h, but in 52.9% of the hips reduced more than 6 h after the injury. Dislocations were classified according to Stewart and Milford [11]; a significantly higher incidence of avascular necrosis was found in grade-III and -IV dislocations than in grade-I and -II dislocations. We could not demonstrate any benefit from skeletal traction or non-weight bearing. The age of the patients was of no importance.