OBJECTIVES: The aim of this study was to determine the frequency and circumstances of the occurrence of sepsis in critical patients treated at the Intensive care unit and to evaluate the severity of sepsis due to the degree of the damage of the function of vital organs. SUDY DESIGN: Retrospective study. PARTICIPANTS AND METHODS: The respondents were adult patients treated at the Intensive care unit at Clinical Hospital Center Osijek over a period of two years. Demographic and clinical data on the respondents were collected from the respondents’ medical history and data on pathogens were taken from the microbiological protocol. RESULTS: Sepsis was found in 99 respondents. In 62 respondents, it was established at the time of admission, while in 44 respondents it was found during their stay at the Intensive care unit. The majority of the respondents reported the dysfunction of the respiratory system. Most of the respondents were surgical patients. In 39 % of cases sepsis source were intraabdominal infections, and in 30 % of cases source were respiratory infections. In 58 % of cases the causes of sepsis were resistant hospital microorganisms. 70 % of the respondents with confirmed sepsis died. When the new critera were taken into concideration, sepsis was found in 58 % of the respondents. Statistically significant difference was not found in SOFA score between "septic" and "non-septic" respondents, but the latter had more favorable outcome of the treatment. CONCLUSION: Surgical treatment and emergency operation are key risk factors for sepsis on the admission to the Intensive care unit. Sepsis outbreaks are most common in intraabdominal and respiratory infections, while pathogens are often resistant hospital microorganisms. Septic patients with severe sepsis and septic shock were isolated according to the new definition of sepsis criteria. Subjects without confirmed sepsis had more favorable outcome of the treatment.