Piperacillin/tazobactam is a commonly prescribed antibiotic and is generally considered safe. We report a case of a 2-year-old girl who developed hypokalemic metabolic alkalosis and bradycardia after receiving intravenous piperacillin-tazobactam for bronchopneumonia. Upon withdrawal of the drug, serum potassium normalized in 2 days. Hypokalemia is a serious adverse effect of piperacillin-tazobactam and should be suspected while treating patients with this drug. Early recognition and prompt withdrawal of the drug will result in lesser morbidity.