PURPOSE: The aim of this study was to investigate the overall rate of deep infection and the risk factors for infection after primary total knee arhroplasties. MATERIALS AND METHODS: We conducted a retrospective case-control study of 229 patients (376 knees) who underwent total knee replacement (TKR) between January 2006 and June 2007 and who were followed up for more than one year. The risk factors for deep infection were determined via univariate analyses. RESULTS: The overall rate for developing infection was 1.9% (7 of 376). The risk factors were an operating theatre other than the main room (odds ratio=33.2, 95% confidence interval=1.9, 583.6) and a preoperative hemoglobin level lower than 12 mg% (odds ratio=4.3, 95% confidence interval=1.9, 9.4). CONCLUSION: The deep infection rates after TKRs might vary depending on the preoperative level of hemoglobin and the operating-room environment. Successful strategies to overcome the host and environmental risk factors are needed with the goal of preventing infection of the prosthesis.