Traumatic myosistis ossificans is a reactive lesion occurring in soft tissues and at times near bone and periosteum. Twenty-four cases of traumatic myositis ossificans of the lower extremity were analysed dinically and radiologically who were treated at the Department of Orthopedic Surgery, Capital Armed Forces and Dae Jun Armed Forces General Hospital during the 3 years period from January 1977 to December 1980. The results were as follows; 1. The causes of trauma consisted of 11 football, 5 falling & slipping, 3 traffic accidents, 2 running, 2 working & training and 1 stick injury. 2. The earliest noticeable x-ray change was found on the 19th day (Mean: 25th day), 3. Soft tissue injuries in all cases were grouped according to the severity of trauma as mild, moderate, and severe. Myosities ossificans occured only in moderately and severely injured cases. The mean size of the calcified mass in severe cases was 23.9cm² and was larger than that of moderate cases, and more lengthy treatment was required in severe cases; it required 2 weeks more than that of moderate cases. 4. One-third of all cases sustained reinjury. The mean size of the calcified mass of these 1/3 cases was 44.4cm² and was larger than that of the mean size of all cases and more lengthy treatment of these 1/3 cases was required in reinjuried cases; it required 1.8 weeks more than that of all cases. 5. In those patients presenting after 3 weeks from injury, the mean size of the calcified mass was 37.6cm² and was larger than that of those patients presenting within 3 weeks. Mean duration of treatment was 13.1 weeks in those patients presenting after 3 weeks, and 10.2 weeks in those patients presenting within 3 weeks. This figure suggest that early treatment is preferable in minimizing the size of the ossifying mass and shortening the duration of treatment.