Surgical site infections on surgical wards are the most common cause of postoperative complications. Prevalence of surgical site infections depends on the surgical specialization. Analysis of the causes of surgical site infections allows to conclude that microorganisms from the patient’s own microbiota – Gram-negative rod-shaped bacteria from the family Enterobacteriacae and from the patient’s skin microbiota – Gram-positive cocci – Staphylococcus are the most common agents inducing surgical site infections. The aim of the study was to assess prevalence and characteristics of surgical site infections caused by Gram-negative rod-shaped bacteria from the family Eneterobacteriacae and Gram-positive cocci from the genus Staphylococcus in patients who underwent surgical procedures at the Regional Specialist Hospital named after M. Copernika in Łódź on selected surgical wards. Material and methods. The study was performed based on retrospective analysis of medical documentation of the treated patients. The study included 195 patients of the Regional Specialist Hospital named after M. Copernik in Łódź who were treated between 2012 and 2014 on the wards of: Vascular, General and Oncological Surgery, Trauma and Orthopaedic Surgery, Neosurgery and Nervous System Tumors and the Ward of Endocrine Surgery – in the Clinic of Endocrine Surgery. The study included 84 women and 111 men. Mean age was 59 years (18 – 94 years old). \ Results. Surgical site infections caused by Gram-negative rod-shaped bacteria from the family Enterobacteriacae were reported in 84 out of 195 patients (43.08% of the study group) and by Gram-positive cocci from the genus Staphylococcus were reported in 52 patients (26.67% of the study group). Mixed microbiota was an etiological agent of surgical site infections in four patients (2.5% of the study group). Conclusions. Etiological agent of surgical site infections depends on the ward profile, surgical field cleanliness and a form of surgical site infection.