The clinical and microbiologic characteristics of 29 episodes of sepsis caused by Acinetobacter calcoaceticus were reviewed in 25 children with underlying malignancies. Of the 29 episodes of sepsis with this organism 28 occurred from 1980 through 1984, compared with 1 episode from 1973 to 1979. Risk of infection was associated with the presence of intravascular cannulae, osteosarcoma and recent administration of antitumor chemotherapy. There was no association with neutropenia, malnutrition or focal infection. Of 28 organisms for which the biotypes were known, 14 (50%) were var. lwoffi and 14 (50%) were var. anitratus; 11 episodes (38%) were part of a polymicrobial bacteremia. All patients responded favorably to antimicrobial therapy.