BACKGROUND : As Japan has an aging population, elderly patients with multiple complicating comorbidities have increased in number. The purpose of the present study was to examine the 90-day mortality and reoperation rate after emergency amputation of the lower limbs and to clarify patient characteristics and preoperative comorbidities that are risk factors for reoperations. METHODS : This retrospective case study was conducted between January 2005 and December 2017. Ninety-one patients with 108 limbs who had undergone emergency amputation of the lower limbs were included in this study. Baseline data, medical comorbidities, surgical procedures and laboratory data including C-reactive protein (CRP), white blood cells (WBC) and hemoglobin A1c (HbA1c) were evaluated. Outcome measurements were mortality, reoperation rate, and factors associated with reoperation in 90 days and any complication after amputation of the lower limbs. RESULTS : The patients (male/female ratio = 64/27) had a mean age of 64.9 years, a mean WBC count of 16,747/μL, a mean CRP value of 15.6 mg/dL, and a mean HbA1c value of 7.5%. The 90-day mortality rate in the study population was 12.1%. The 90-day reoperation rate was 35.2% (32/91) patients with 32.4% (35/108) limbs. The factor significantly associated with reoperation in 90 days was peripheral arterial disease (PAD) (p = 0.022, HR = 2.75), identified with Cox proportional hazards regression analysis. A total of 41.8% (38/91) patients with 40.7% (44/108) limbs experienced postoperative wound complications. The overall rate of medical complications was 18.7% (17/91) patients with 16.7% (18/108) limbs. CONCLUSIONS : This study indicates that the 90-day mortality and reoperation rates after emergency amputation of the lower limbs were high. Furthermore, PAD influences the rate of reoperation in 90 days. However, there was no association between laboratory results or diabetes mellitus and reoperation. These findings will have important implications for the treatment of lower leg amputation and prevention of reoperation.