PURPOSE : The goal of this study is to decrease the chance of the lower limb loss resulting from the delayed diagnosis of arterial thrombosis after first operation in a patient of the closed fractures around the knee by early diagnosis and proper management via studying several prognostic factors. MATERIALS AND METHODS : We have reviewed 8 cases of delayed diagnosed arterial thrombosis patient who was follow up for 1 year or more March 1987 to February 1997, retrospectively. We have followed ip the clinical results. RESULTS : The amputation rate was 50%(4/8), and among associated injuries, tibial or peroneal nerve palsy was combined in 75%(6/8). The time interval from initial trauma to diagnosis was significantly different between amputation group(77hours) and non amputation group(34.25hours). Better results were obtained in cases who had early diagnosis and treated with end to end anastomosis than vein graft. CONCLUSION : It is very important that the vascular status should be assessed not only at the first examination but also repeatedly over the ensuing hours and days with caution, even though there was absence of ischemic sign.