BACKGROUND Problems, consequences and influence of immobilization on tissue and fracture healing, as well as patient's psyche and entire condition of the organism, are well known. With immobilisation patient looses a part of extremity movement. Healing of fractures and remaining tissues is a natural process, so it is usually said that fractures and tissues heal not because of immobilization, but in spite of it. The theory of treating by functional cast (PTB-patellar tendon bearing), firstly described by Sarmiento, is based on tissues natural capability to heal and on its functional guiding to the final cause. The aim of this study is to analyze our previous expirience in regard to this method. METHODS We have studied patients from 7 to 70 years of age with fracture of one or both lower leg bones. After injury, patients were mobilized using upper leg plaster impregned bandages applied to two thirds of extremity's circumference. After X-ray control and locating the position of broken parts, patients were released with thromboprophylaxis using Acetilsalycil acid (Midol) 3 x 1 tablet per day. In some cases, where reduction of broken fragment was hard, total anesthesia was performed. In cases of oblique and spiral fractures, because of possible redislocation we have waited with application of lower leg functional cast up to 3 weeks. RESULTS We have studied 59 patients, most of them between the age of 11 and 20. In most cases functional cast was applied after 21 to 30 days, fractures healed after 90 to 99 days and the shortening of extremities was clinically non measureable. Usually it was 24 mm. CONCLUSIONS Treatment of lower leg fractures is not simple. We especially point to problems with circulation and skin which have to be controlled over and over. There are reports of rejecting operational method as a method for lower leg fracture treating. Our results are the same as those achieved by other authors. Reposition of bone fragments must be performed with special attention. It is best if it is performed during total anesthesia, because muscles are relaxed and therefore circulation gets better, intensity of pain decreases and there are no skin necroses. In few cases, at the beginning of treatment there were skin blisters which only lengthened the treatment. These problems were prevented by early reposition, retention of bone parts and elevation of extremities. CONCLUSIONS Lower leg functional cast gives excellent results in treating diaphyseal lower leg fractures. Early mobilization positively influences the patient's psyche and enables quick resocialization. Physical treatment is usually not necessary.