The head patient with musculoskeletal trauma is a challenge to the orthopedic surgeon and its incidence is increasing markedly with the development of modern culture and a high velocity motor vehicle. So, for the purpose of studying the difference between lower extremity fracture concomitant with head injury and only lower extremity fractured patients, we studied the radiologic bone union time, serologic test and heterotopic ossification. For the control group we analysed each 10 patients of only femur and tibia fractures. The following clinical results were obtained by analysis of 46 patients of lower extremity fracture concomitant with head injury, experienced in the Department of Orthopedic Surgery, Yonsei University College of Medicine in past 5 years from Jan. 1980 to Dec. 1984. 1. The mean age was 24.5 yrs old (2~6 yrs old) and the prevalent age was 1st and 3rd decade, and the sex ratio between males and females was 2.8: l. 2. The most common mode of injury was auto-pedestrian injury (84.8%) and the other was falling down injury(15.2%) . 3. The common brain injuries were cetebral contusion with skull fracture (37.0%) and cerebral contusion only(34.8%). Among 26 patients whos mental states were not alert, 23 patients recovered mental states completely. 4. Serum Calcium, Phosphate, and Alkaline Phosphatase level were no difference between the head injury with lower extremity fractured patients and only lower extremity fractured patients. 5. There were no evidence of early bony union in the patients with head injury. 6. The formation of callus were abundant in the patients of lower extremity fracture with head injury rather than the only lower extremity fractured patients. 7. The incidence of heterotopic ossification was 10.9% and all patients with heterotopic ossification were treated with physiotherapy and all patients recovered fully. 8. The incidence of complication was 17.3% and there was no fat embolic patients. In conclusion, there was no evidence of early bony union, but the callus formation was abundant in the patients of lower extremity fracture concomitant with head injury.