Background & Objectives: Nosocomial infections occur following admission of patients in the hospitals and usually are accompanied by significant mortalities. This study was conducted to determine the frequency of nosocomial infections and the causatives in Ardabil Bu Ali hospital during 2010.

  Methods: This study was a cross-sectional study which has been done on collection of information through practical examinations, laboratory tests and files of nosocomillay infected patients in Ardabil Bu Ali hospital during 2010. Data were analyzed by SPSS.

  Results: From a total of 3254 patients, 42 (1.3%) had got nosocomial infections. Of these infected patients 47.6% was males and 52.4% was females. Infection was more frequent in patients with ages between 1 month to1 year old (45.2%). Sepsis (33.3%), pneumonia and blood stream infections (23.8%) and urinary tract infection (19%) were the most frequent infections. The mean length of hospital stay was 26.86 days. Klebsiella pneumoniae was the most common pathogen reported (23.8%). Infection was more common in NICU (38.1%).

  Conclusion: In this study, the frequency of nosocomial infection was lower than other studies. Distribution of infection differed with age, ward and length of stay in the hospital.