A survey was carried out of all urinary tract infections which developed bacteremia during an 18 month period. The number of episodes of bacteremia of urinary origin (BUO) detected in our institution during that period was 108. The urinary tract was the most common origin of the cases of community acquired (CA) bacteremia and the third in the hospital acquired (HA) cases. In both types, the most frequent organism was E. coli (69.6% and 40%, respectively). The most common underlying diseases were diabetes mellitus (25.7%) and neoplasia (20%); nephrourologic disorders of some type were present in 29.6% of cases. In 81% of HA episodes there were urinary catheters as risk factors. In the CA bacteremias, the gram-negative bacilli except Pseudomonas aeruginosa had a 100% sensitivity to aminoglycosides. Sensitivity to first generation cephalosporins was detected in 81% of the E. coli and in 100% of the Klebsiella spp strains. In HA cases, amikacin (100% of E. coli, Pseudomonas, Klebsiella and Proteus) and cefotaxime (except Pseudomonas) were the antibiotics to which the highest rates of sensitivity were found. Overall mortality rate of BUO was 16.6% (13.6% for CA and 21.5% for HA); in 6% and 5% of cases, respectively, death was directly associated with bacteremia.