Surgical treatment for severe slipping of the upper femoral epiphysis. We have used a modified technique of cervical osteotomy to treat a consecutive series of 23 patients with chronic slip of the upper femoral epiphysis. It has been successful in correcting both moderate and severe deformities with a low incidence of avascular necrosis, comparable to that seen after subtrochanteric osteotomies. We describe the operative details and discuss the features which make cervical osteotomy technically superior to intertrochanteric and subtrochanteric procedures. 