Surgical site infections (SSI) are one of the most frequent and serious complications in contemporary surgery. The incidence of SSI depends on a variety of factors, knowing which enables targeted preventive measures to be employed. Under currently effective legislation, an infection risk assessment must be entered into a patient’s medical documentation upon admission. The infection risk assessment should take into account both risk factors related to the patient and to the surgical treatment itself (preoperative, perioperative and postoperative). SSI risk factors may also be classified as modifiable and non-modifiable ones, and if their incidence in individual patients is known it has a considerable influence on reducing the number of infections. The article discusses surgical site infection risk factors with particular emphasis on modifiable factors.