BACKGROUND Diabetic foot lesion is associated with increased morbidity and high resource use. Although early amputation has been advocated in case of osteomyelitis, conservative treatment is a more attractive alternative. OBJECTIVE To identify criteria predictive of failure of conservative treatment of diabetic foot ulcer at time of admission to the hospital. METHODS We conducted a 5-year retrospective cohort study with prospective long-term follow-up of all diabetic patients admitted for a foot lesion at a large (1600-bed) teaching institution. Predetermined criteria were used for the diagnosis and classification of diabetic foot lesions (Wagner classification). Study variables included patient demographics and clinical parameters related to infection and diabetes. The average follow-up after hospital discharge was 2 years. Failure of conservative treatment was the main outcome measure. Independent predictor variables were selected by logistic regression analysis. RESULTS A total of 120 diabetic patients were admitted for foot lesions; complications of contiguous osteomyelitis, deep tissue involvement, and/or gangrenous lesions occurred in 78 (74%) of the 105 patients for whom charts were available. Fourteen patients (13%) underwent immediate amputation. Conservative treatment was successful for 57 (63%) of the 91 remaining patients. Success was achieved in 21 (81%) of 26 patients presenting with skin ulcer, 35 (70%) of 50 patients with deep tissue infection or suspected osteomyelitis, and 1 (7%) of 15 patients with gangrene (P<.001, chi2 for trend). Independent factors predictive of failure were the presence of fever (odds ratio [OR]=1.1 per degrees Celcius; 95% confidence interval [CI], 1.0-1.2) and increased serum creatinine level (OR=1.002 per micromoles per liter; 95% CI, 1.0020-1.0021) on admission, prior hospitalization for diabetic foot lesion (OR=1.4; 95% CI, 1.2-1.6), and gangrenous lesion (OR=1.8; 95% CI, 1.5-2.2). Other patient characteristics, demographics, duration of diabetes mellitus, neutrophil count, or the anatomical site of the lesion failed to predict outcome. CONCLUSIONS Conservative treatment, including prolonged, culture-guided parenteral and oral antibiotics, is successful without amputation in a large proportion of diabetic patients admitted for a foot skin ulcer or suspected osteomyelitis. Future studies comparing early amputation with novel therapeutic strategies for severe diabetic foot infection should take into account currently identified factors that predicted failure of conservative treatment on admission to the hospital.