The medical records of 27 patients with blood cultures positive for Acinetobacter calcoaceticus over a recent five-year period (0.7% of all positive blood cultures) were reviewed retrospectively to determine the epidemiologic and clinical significance of these isolates. Eighteen isolates represented true bacteremias, 16 of which were hospital acquired. Patients most frequently were located in an intensive care unit or on a surgical ward. A seasonal July-to-September peak incidence was noted. The most common site of primary infection was the respiratory tract. Aminoglycosides, alone or in combination with a second agent, were used to treat all but one infection. Bacteriologic cure was achieved in 15 cases (88%); six patients had polymicrobial sepsis that carried a higher mortality than pure A calcoaceticus bacteremia (50% vs 0%). Acinetobacter, a low-virulence opportunistic pathogen, may be an infrequent but potentially serious endemic agent of nosocomial bacteremia in some institutions. The prognosis of bacteremia, when appropriately treated, appears to be good.