OBJECTIVE To identify risk factors associated with an outbreak of gram-negative bacteremia (GNB). METHODS A university hospital. METHODS Hematology-oncology outpatients. METHODS Retrospective case-control study. RESULTS Thirty-eight patients developed GNB; 13 patients experienced more than one episode, and eight blood cultures grew more than one gram-negative organism. The most frequently isolated organisms were Stenotrophomonas maltophilia, Klebsiella pneumoniae, Acinetobacter baumannii, and Acinetobacter johnsonii. When the GNB patients (cases) were compared with randomly selected hematology-oncology patients (controls), central venous catheter (CVC) self-care (71% vs 39%; P=.02), and duration of recent hospital stay (median, 15 vs 4 days; P=.01) were identified as risk factors. In a logistic regression model, duration of recent hospital stay was the only risk factor significantly associated with GNB (odds ratio, 1.05; 95% confidence interval, 1.01-1.08; P<.02). CONCLUSIONS Hematology-oncology patients providing their own CVC care who have recently been hospitalized for more than 2 weeks may be at increased risk of GNB. CVCs should be protected from possible environmental contamination in hematologyoncology patients. Patients providing their own CVC care should undergo continued rigorous education regarding proper CVC care.