The beta-lactam/beta-lactamase inhibitor combinations are a good choice for empirical antimicrobial therapy in febrile neutropenic patients, because their antibacterial spectra include both gram-negative and gram-positive pathogens. This trial was initiated to assess the efficacy and safety of piperacillin with the beta-lactam inhibitors sulbactam (PSG group) or tazobactam (PTG group) and gentamicin as initial therapy in febrile neutropenia of pediatric patients. In a prospective study, 239 episodes of fever and neutropenia were analyzed for the clinical and microbiological response dependent on infection etiology and treatment group: 66.5% of episodes were classified as fever of unknown origin (FUO) and 33.5%, as microbiologically or clinically documented infections; 19.2% of all episodes were due to bacteremia, predominantly caused by gram-positive organisms (69.6%). The response to the initial therapy was 55.2% overall and 65.4% in episodes of FUO with a significant higher success rate in the PSG group than in the PTG group (70.1% vs. 52.4%, P=0.039), and 35.0% in documented infections. In episodes with documented infection longer duration of fever and antimicrobial therapy was recorded than for FUO episodes. Four patients died of causes related to infection. Fever relapse occurred in 26 episodes (11.1%), predominantly in patients who were still neutropenic. Toxic side effects were minimal. The initial therapy of piperacillin with sulbactam or tazobactam in combination with gentamicin is well tolerated, and its efficacy is comparable to that of other combination therapies or of monotherapy with beta-lactam antibiotics in pediatric neutropenic cancer patients.