One hundred and seventy hospitalized patients with cirrhosis were included in a prospective and sequential study, to verify the prevalence and most frequent causes of bacterial infection. The differences in clinical and laboratory data between the two groups were analyzed: group I--80 patients who developed bacterial infection and group II--90 patients without bacterial infection. The prevalence or cumulative frequency of the development of bacterial infection during one hospitalization was 47.06%. Among these, the most frequent types of infection were: spontaneous bacterial peritonitis (SBP): 31.07%, urinary tract infection (UTI): 25.24% and pneumonia: 21.37%. Community infections were more frequent (56.25%) than nosocomial infections (32.50%) and they occurred sequentially in 11.25% of the cases. The agents responsible were gram negative bacteria in 72.34% of the cases. Clinical and biochemical parameters in bacterial infection were generally correlated with the severity of liver disease. Child-Pugh classification showed a predominance of class C in infected cirrhotic patients compared to non-infected ones. During hospitalization, the mortality rate of group I was 30% whereas in group II it was 5.55% (P = 0.0001). SBP and pneumonia were the most severe types of infection, with high mortality rates, 31.25% and 40.91%, respectively. These results indicate that bacterial infection is a severe complication in the course of cirrhosis.