Avascular hip necrosis is a disease which occurs as the consequence of ishemia of a part of the femoral head. Ishemia most often occurs on the most burdened part of the femoral head. The affected part softens and gradually collapses. The burdening surface of the head reduces and the contact joint stress increases. This results in premature arthrotic changes. The diease affects younger population, most often the patients undergoing a long-lasting corticosteroid therapy, and chronic alcoholics. The development of the disease depends greatly on biological as well as biomechanical factors. An early diagnosis is important for the successful treatment of the disease. At an early stage the disease is treated with decompression. A moderately advanced stage is treated with intertrochanteric osteotomy and with the fully damaged femoral head the only sensible solution is the hip replacement.