The indications for treatment of idiopathic necrosis of the hip depend on the stage of development of the lesion, its extent and the site of the necrotic area. Digital computerised tomography with horizontal sections at five millimetre intervals from the upper to the lower pole of the femoral head is of value in the determination of these three features. For this purpose, fifteen femoral heads removed in the course of total hip arthroplasty were subjected to histological sections in parallel to those of the CT scan. This study showed that digital computerised tomography indicates the extent and topography of the necrosis and provides true histo-radiological sections.