In a prospective study carried out in June 1979-April 1981, 134 of 1,458 adult inpatients at New England Deaconess Hospital, Boston, Massachusetts, acquired 136 urinary tract infections during 1,474 indwelling bladder catheterizations. Multiple logistic regression analysis identified nine factors that were significantly associated with acquisition of infection: duration of catheterization, lack of systemic antibiotic during short catheter courses, lack of urinemeter drainage, female sex, diabetes mellitus, microbial colonization of the drainage bag, serum creatinine greater than 2 mg/dl at the time of catheterization, the reason for catheterization, and the use of catheters with sealed collection junctions when no antibiotic was administered. When potential risk factors were considered individually, without adjusting for the influence of other factors, infection was also significantly associated with 11 other factors, including several that have been previously reported as risk factors for catheter-associated urinary tract infections; however, these associations were no longer significant after adjustment for one or more of the nine factors noted above. These findings suggest approaches to surveillance, prevention, and research activities. They also strongly support the widely-held but poorly documented belief that persons with diabetes are more susceptible to urinary tract infection than are persons without diabetes.