PURPOSE: The goal of our study was to evaluate diagnosis and management of stress fracture in long bones using MRI findings. MATERIAL & METHOD: Between May 1995 to May 1999, 40 patients( 45 cases ) were confirmed to have a stress fracture by clinical and radiological findings. All patients were evaluated with clinical, X-ray, bone scan, and MRI findings. The patient was 21 years in average( range from 18 to 23 years ). All were males and soldiers. The evaluation was made by comparison of MRI and plain radiograph, and duration of symptom was evaluated with MRI grading by Fredericson et al. RESULT: The locations of stress fracture of long bones were tibia(n=25), fibula(n=14), and femur(n=6). MRI findings were bone marrow edema in 38(84.4%)cases, intramedullary low signal intensity band in 19(42.2%)cases which was continuous with cortex and cortical fracture line. Periosteal reaction was seen in 45(100%)cases and surrounding soft tissue edema in 20(44.4%)cases. Plain X-ray findings were peristeal reaction in 31( 68.9%)cases, medullary sclerosis in 10(22.2%)cases, and cortical fracture line in 8(17.8%) cases. Duration of symptom was longer in higher MRI grade. CONCLUSION: MRI was more useful in early diagnosis and differential diagnosis of stress fracture, showing various findings than plain radiograph. MRI grading was helpful in planning tlhe therapy of stress fracture.