Despite the fact that breast operations are usually categorized as clean procedures, higher surgical site infection (SSI) rates are reported. This study aimed to determine the perioperative variables related to SSI in breast cancer patients. Medical records of breast cancer patients undergoing surgery between January 2005 and August 2007 at a university based hospital were reviewed. Preoperative, intraoperative, and postoperative clinical data from 199 patients were extracted and analysed. Overall, the SSI rate was 19.1% (38 cases). SSI was associated with a high body mass index (P=0.001), history of diabetes mellitus (P<0.0001), smoking (P<0.0001), or active skin disorders (P<0.0001). Other SSI-related variables included a tumour at an advanced clinical stage (P=0.003) and neoadjuvant therapy (P=0.003). Breast-conserving operations were less frequently associated with SSI than were radical procedures (mastectomy alone and mastectomy followed by immediate reconstruction) (P=0.0001). © 2011 The Healthcare Infection Society.