ObjectiveTo compare the technical aspects, operative time, safety and effectiveness of percutaneous nephrolithotomy (PCNL) in the free-flank modified supine position (FFMSP) vs. the standard prone position (SPP).Patients and methodsSeventy-seven patients (47 men and 30 women) with renal stones were enrolled and systematically randomised into two groups, A (39 patients) treated using the FFMSP, and B (38 patients) in the SPP. The outcome was considered as a cure (successful procedure) if the patient became stone-free or had residual fragments of <4 mm in diameter. The operative time (from the induction of anaesthesia to the removal of the endotracheal tube) was measured and any operative complications or conflicts were recorded. The different variables were compared and analysed between the groups.ResultsPatients in both groups had comparable preoperative clinical data and there were no significant differences in the preoperative clinical characteristics. The procedure was successful in 84.6% and 84% of group A and B, respectively. The operative time was significantly longer in group B (SPP) than A (FFMSP). There was no significant difference between the groups in fluoroscopy time and patients’ outcome.ConclusionsThe FFMSP (with a cushion under the ipsilateral shoulder) has similar efficacy and safety as the SPP for PCNL and is associated with a significantly quicker operation.