The incidence of bacteriuria and the risk factors related to its acquisition were determined in a prospective study of 220 hospitalized patients. Bacteriuria was recorded in 97/220 (44%) of patients, in 42 cases within 48 h (Group A) and in 55 cases more than 48 h (Group B) after catheterization. The results of a multivariate analysis of Group A demonstrated that the reason for catheterization, the use of antimicrobial chemotherapy and the medical specialty of care were the only variables of those assessed associated with the acquisition of bacteriuria. In a similar analysis of Group B the number of days the catheter was in situ and the use of antimicrobial chemotherapy were the only factors which achieved statistical significance.