Forty episodes of nosocomial Acinetobacter calcoaceticus bacteremia produced by the Anitratus type over a period of 4 years were analyzed and compared with a control group of 28 patients with bacteremia produced by gram negative bacilli. Although most of acinetobacter bacteremia were endemic an outbreak involving 12 cases were observed in an intensive care unit during the study period. Thirteen patients presented a transient bacteremia. When the site of origin of the infection could be established the respiratory system was the most commonly involved (5 cases). Polymicrobial bacteremia was present in 11 patients (27.5%). Gram-positive cocci were the most commonly associated microorganisms. Most of isolated Acinetobacter strains were resistant to cotrimoxazole, beta-lactams, and aminoglycosides but were uniformly sensitive to ciprofloxacin and imipenem. The overall mortality was 22.5%. As compared with the control group, Acinetobacter bacteremia occurred more frequently during the first week of hospitalization and involved patients with less severe underlying diseases in whom three or more potential risk factors were detected. The entering site of infection was commonly unknown and the antibiotic treatment was inappropriate in most of the cases of Acinetobacter bacteremia.