The author reports on symptoms, therapy and results of a follow-up of 17 patients with the rare disease of osteonecrosis of the medial femoral condyle. The therapy depends on the extend of the necrosis, the axis of the leg and the results of scintigraphy or scintimetry and arthrography or arthroscopy. Small necroses can be treated conservatively, but in case of a genu varum a valgus-osteotomie should be performed. Bigger necroses are bored or bolted combined with a valgus-osteotomie, if necessary. Extensive osteonecroses can only be treated by partial endoprosthesis or autologue bone-cartilage-transplantation.