Background: Infections in orthopedic procedures are difficult to eradicate and persist until the implant removal.Methods: Control-case study of 390 patients who underwent to primary hip and knee arthroplasty, from January 2007 to December 2011 at the Hospital and Clinics, Federal University of Minas Gerais. Risk factors and frequency of surgical site infection (SSI) were assessed, beyond the clinical outcome after a year of procedure. Results:In 16 cases of infection, we observed that obesity has configured as a risk factor, and the preoperative bathing as a protective factor for ISC. The SSI rate was approximately 4% and the main microorganisms identified were Gram-negative, especially Acinetobacter baumannii to carbapenems. From infected patients, 85.7% underwent revision of prosthesis in two surgical times and there were no associated deaths. Conclusion:Obese patients have a higher risk for developing SSI and the found rates are above the reported in the literature, probably associated with the greater number of Gram-negative bacteria.