This study compared the effectiveness of the neutrophil/lymphocyte ratio (NLR) versus C-reactive protein (CRP) for evaluating the prognosis and degree of inflammation in patients with amputation for a diabetic foot ulcer (DFU). This study enrolled 56 patients with amputations for DFU with gangrene and compared the CRP levels and NLR measured before and after surgery. Overall, 24 patients (42%) died within 2 weeks postoperatively. Mortality increased with a preoperative/postoperative CRP difference ≤1.5 (P < .001) and age 73 years or older (P < .001). The postoperative NLR was lower than the preoperative value but was not significant as a prognostic or inflammatory marker (P = .945). An increasing serum CRP level is a significant predictor of mortality. CRP and old age are reliable prognostic factors in patients with DFU.