Abstract The clinical records of 66 consecutive episodes of Gram-negative bacteremia occurring in 60 patients with hematologic malignancies during a 66-month period were reviewed to assess the major prognostic factors. The bacteremia-related mortality was 53%. Overall, Pseudomonas aeruginosa (54%) and Escherichia coli (24%) were the predominant isolates (fatality rate 78 and 31%) respectively). The majority of patients ( 58 66 ) were granulocytopenic (PMN < 1000/μ l). Among the 18 patients whose circulating granulocytes increased by one log 10 or to above 1000/ mmc during therapy, the fatality rate was 39%, as opposed to 70% in the 40 patients without such an increase. Pneumonia-associated bacteremia (56%) had a high fatality rate (73%) compared to isolated bacteremias (27%). Septic shock and inappropriate antibiotic therapy accounted for the highest mortality. Our data suggest that Pseudomonas etiology, persistent neutropenia, associated pneumonia, septic shock and inappropriate antibiotic therapy account for a bad prognosis in Gram-negative bacteremia in hematologic malignancies.