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Objective: To test the hypothesis that the addition of an aminoglycoside to a ß-lactam antibiotic could provide better outcomes than ß-lactam monotherapy for the initial empirical treatment of hematological neutropenic patients with subsequently documented Gram-negative bacilli (GNB) bloodstream infection (BSI). Methods: Multinational, retrospective, cohort study of GNB BSI episodes in hematological neutropenic patients in six centers (2010–2017). Combination therapy (ß-lactam plus aminoglycoside) was compared to ß-lactam monotherapy. The primary endpoint was the case-fatality rate assessed at 7 and 30-days from BSI onset. Secondary endpoints were nephrotoxicity and persistent BSI. Propensity score (PS) matching was performed. Results: Among 542 GNB BSI episodes, 304 (56%) were initially treated with combination therapy, with cefepime plus amikacin being most common (158/304, 52%). Overall, Escherichia coli (273/304, 50.4%) was the main etiological agent, followed by Pseudomonas aeruginosa, which predominated in the combination group [76/304 (25%) vs. 28/238 (11.8%); p<0.001]. Multidrug resistance rates were similar between groups [83/294 (28.2%) vs. 63/233 (27%); p=0.95]. In the multivariate analysis combination therapy was associated with lower 7-day case-fatality rate (OR 0.37, 95%CI 0.14-0.91;p=0.035) with a tendency towards lower mortality at 30 days (OR 0.56, 95%CI 0.29–1.08;p=0.084). After PS-matching, these differences remained for the 7-day case-fatality rate (OR 0.33, 95%CI 0.13–0.82;p=0.017). In addition, aminoglycoside use was not significantly associated with renal function impairment (OR 1.12, 95%CI 0.26–4.87;p=0.9). Conclusions: The addition of an aminoglycoside to the initial empirical therapy regimen for febrile neutropenic hematological patients should be considered.