Laparoscopic surgery is an evolving surgical modality in children, which has been applied to increasingly more complex surgeries and patients, including patients with renal insufficiency. These patients are particularly susceptible to the challenges that laparoscopy imposes on their altered physiology, leading to marked electrolyte disturbances, including metabolic acidosis and hyperkalemia. Hyperkalemia has the potential for marked impairment of cardiac conduction. We report 2 cases where significant, potentially lethal hyperkalemia developed during laparoscopic nephrectomy in adolescents with renal insufficiency. Awareness of this issue, as well as adequate preparation and intraoperative monitoring are essential to preventing this life-threatening complication.