Bacground/Aim. Nosocomial infections (NIs) are an important cause of morbidity, mortality and prolonged hospitalizations. Fifty percent of NIs have been reported in Intensive Care Units. The aim of this study was to determine the frequency and type of NIs among critically ill patients treated in the University Hospital for Infectious and Tropical Diseases, Clinical Centre of Serbia, as well as risk factors for acquiring them. Methods. This prospective cohort study included 52 patients treated in the Intensive Care Unit from January to June 2004. The diagnosis of NI was established according to the Centers for Disease Control and Prevention (CDC) definition, based on clinical presentation, radiological and microbiological findings, etc. Statistical data processing was done by using the electronic data base organized in SPSS for Windows version 10.0. The level of statistical significance was defined as p < 0. 05. Results. NIs were found in 33 (63.4%) of 52 inpatients. Urinary tract infections (UTIs), pneumonia, and soft tissue infections, the most common nosocomial infections in our setting, were recorded in 41.0%, 25.6%, and 23.1%, of patients, respectively. Several factors contributed to a high incidence of these infections: chronic comorbidities (p < 0.01), the presence of indwelling devices such as urinary tract catheters (p < 0.01), endotracheal tubes (p < 0.05) along with mechanical ventilation (p < 0.05). Conclusion. The majority of patients with NIs had chronic underlying comorbidities. All the patients with UTIs had urinary catheters. The most important risk factors for the development of nosocomial pneumonias were endotracheal intubation and mechanical ventilation. The patients with pneumonia had the highest mortality.