Background and purpose: Nosocomial infections are among the main causes of death among hospitalized patients. Successful control of these infections requires awareness on their prevalence and taking preventive measures in hospitals. This study aimed at determining the prevalence of hospital-acquired infections in Mazandaran province. Materials and methods: A descriptive-longitudinal study was performed in 15 hospitals in Mazandaran province that record their infection rates in NISS software. Data was analyzed at the significance level of 0.05 using SPSS and STATA software. To investigate the relationships between different variables crosstabs and Poisson regression were applied. Results: The mean ages of infected male and female were 54.53±0.67 and 49.2±0.63 years, respectively (P<0.05). The amount of infections in the 15 hospitals in 2011 was 79% and in 2012, it was 1.21%. The highest incidence of infections was due to pneumonia, urinary infection, surgical incisions, and burn wounds. The majority of infections were caused by Escherichia coli (E. coli) (12.3%), Pseudomonas aeruginosa (6.3%), Acinetobacter (6.1%), and Klebsiella (5.9%). A significant relationship was observed between an underlying disease and various types of infections (P<0.05). The risk of hospital infections in women was 1.09 times more than men (P=0.918). Conclusion: The risk of infection was not significant among women and men. Having a background disease affects the kind of infection. The incidence of infection showed an increase in 2012 compared to 2011..