Summary The aim of the study was to assess the significance of some perinatal risk factors and neonatal complications in occurrence of nosocomial infections in the population of NICU patients. Material and methods: Analysis of risk factors was performed in all patients treated in the years 2005-2008 in NICU Department of the Pomeranian Medical University in Szczecin, Poland. Five hundred and seventeen neonates divided into groups with and without occurrence of nosocomial infection were included into the study. Results: Seventy nine (15.28%) neonates developed nosocomial infection. Among them pneumonia (56.96%) and sepsis (21.5%) were the most common. The proportion of Gram-positive and Gram negative organisms were 44.3% and 50.6% respectively. The main risk factor for nosocomial infection was colonization (sensitivity - 100% and specificity – 94.75%). Univariate analysis showed that premature rupture of fetal membrane, GA< 32 hbd, birthweight <2000g, respiratory insufficiency, intracranial hemorrhages and oral feeding intolerance were associated with the development of nosocomial infection. Multivariate stepwise logistic regression analysis showed that mechanical ventilation – OR 9,42 [4,45-19,96] p<0,0001, intracranial hemorrhages – OR 4,12 [2,21-7,67] p<0,0001, necessity of Infant-Flow method - OR 3,32 [1,82-6,06] p<0,0001or n-CPAP method - OR 1,92 [1,07-3,44] p<0,05, necrotizing enterocolitis – OR 2,38 [1,17-4,87] p<0,05 and intrauterine hypotrophy - OR 1,8 [1,07-3,76] p<0,05 were sets of predicted factors for the development of nosocomial infection. We conclude that colonization of NICU patients with hospital pathogens is the most important risk factor of nosocomial infection incidence. Besides colonization, significant additional risk factors for nosocomial infection were mechanical ventilation, intraventricular hemorrhages, low birth weight and low gestational age.