Background:The aim of this study was to investigate and then to compare the prevalence of nosocomial infections (NIs) in the patients admitted to the surgery and internal Intensive Care Units(ICU) as well as studying the risk factors involved.Methods:In this cross-sectional descriptive, patients admitted to ICUs were studied over a year .Clinical data of patients, including demographic information, length of stay, underlining disease, the rate of patient with NIs and distribution of NIs sites and pathogens were collected. Univariate and multivariate logestic regression were carried out to determine the factors associated with NIs.Results:A total of 1018 patients were studiedincluding surgical ICU (n = 665) and internal ICU (n = 353). The incidence rate of NI in surgical and internal ICUs was 67(10.1%) and 96(27.2%), respectively. The most common NI in the internal ICU were respiratory tract infections( RTI ,46.9%) and urinary tract infections (UTI, 37.5%), while in the surgical ICU, the most common infections were respiratory tract infections (RTI, 38.3%) and surgical-site infections (SSI, 22.0%), respectively. The major factors the length of stay and the use of nasogastric intubation (NG tubes) were associated with NIs in both ICUs.Conclusions:The incidence of infections in the internal ICU were more than the surgical ICU. Age, underlying diseases, the long stay, used of ventilator and NG tube were factors associated with NIs rate in internal ICU.Trial registration:This study was the result of two research works with ethics code (IR.BUMS.REC.1394-17 and IR.BUMS.REC.1394-27).