['To define the risk factors of allogeneic erythrocyte transfusion in patients older than 65 years of age who underwent hip fracture surgery.', 'Retrospective, single-center study.', 'Orthopedic unit of a university hospital.', 'The records of 413 consecutive patients undergoing hip fracture surgery over a 12-month period and receiving low-molecular-weight heparin (LMWH) for thromboprophylaxis were retrospectively reviewed. Preoperative independent predictors of transfusion were determined by multivariate analysis, from which a model of individual probability of transfusion was derived using creatinine clearance calculated by Cockroft-Gault (CG) and the Modification of Diet in Renal Disease (MDRD) formulas.', 'Using the CG and MDRD formulas, 56.9% and 50.1% of patients had moderate renal impairment that was an independent factor associated with transfusion, with adjusted odds ratios of 2.44 (1.49 - 4.02) and 2.35 (1.32 - 4.18), respectively. Other factors were fracture with trochanteric extension, preoperative hemoglobin (Hb) < 12 g/dL, and weight. The observed transfusion rate and probability of transfusion calculated with the regression logistic model were well correlated: y = 0.9534x + 0.0287, P < 0.0001, Pearson coefficient 0.988, goodness of fit, χ(2), P = 1 with CG; y = 0.9197x + 0.0504, P < 0.0001, Pearson coefficient 0.956, goodness of fit, χ(2), P = 1 with MDRD).'] Is preoperative moderate renal impairment an independent risk factor of transfusion in elderly patients undergoing hip fracture surgery and receiving low-molecular-weight heparin for thromboprophylaxis?