We report a significantly higher occurrence of adverse events associated with prolonged courses of piperacillin-tazobactam compared with other antibacterial agents used for pediatric outpatient parenteral antimicrobial therapy. These adverse events were characterized by a constellation of clinical findings including fever, hematologic abnormalities and transaminitis. Adverse events related to piperacillin-tazobactam should be considered in patients who develop a febrile illness associated with a prolonged course of therapy.