In 2-3 reviews 30 patients with non ossifying fibroma and 31 patients with a solitary bone cyst were examined to evaluate the prognosis of these diseases. It has been shown that the cure rate of non ossifying fibromas of 95% and solitary bone cysts of 70% is extraordinarily good and does not depend on the treatment that has been realized. For that reason, the indication for operative treatment must be differentiated: Non ossifying fibromas should be left to spontaneous healing. Solitary bone cysts in the upper limb should be treated by puncture only when they show great activity, otherwise they can be left to spontaneous healing, too. In the lower limb active cysts with or without fracture should be operated, while inactive cysts should to be cured by puncture only.