Objectives: To determine the validity of some criteria that could guide in the decision to cancel or proceed with the second side of planned bilateral simultaneous percutaneous nephrolithotomy (bsPCNL). Methods: Patients with an indication for bilateral PCNL were enrolled in this study. The operation was stopped at the end of the initial side if operative time was >180 min, the hemoglobin level was <11 g/dL, the hemoglobin decrease was >3 g/dL, the systolic arterial pressure was <100 mm Hg, the arterial oxygen saturation was <95%, the arterial blood pH was <7.35, or the blood sodium was <128 mg/mL. The success and complication rates were compared in patients who underwent second side PCNL (group 1) and those for whom the procedure was stopped after the initial side (group 2). Results: Of 42 planned bsPCNLs, 12 were stopped after the initial side, with the cause being prolonged operative time in 7, hemoglobin decrease in 6, systolic arterial pressure decrease in 2, arterial oxygen saturation decrease in 2, pH decrease in 1, and sodium decrease in 1. Differences in patient characteristics, stone burdens, and overall success and complication rates were insignificant. Transfusion, postoperative urinary infection, and prolonged urine drainage rates were similar, but the total hospitalization time was significantly longer in group 2. One hydrothorax and one renal pelvic perforation occurred in group 2. The need for transfusion correlated positively with the number of nephrostomy tracts in group 2 (r = 0.895, P = .001). No such correlation was found in group 1. Conclusions: Despite the best of intentions, about 30% of anticipated bsPCNL cases might be limited to single-sided PCNL, depending on the intraoperative events. Our criteria seem reasonable, because similar success and complication rates were obtained with bilateral, separate-session PCNL and bsPCNL. These criteria can be considered in the decision making to omit the advantages of a single session for safety.