Background: Prone percutaneous nehprolithotomy (PCNL) is associated with patient inconvenience, circulatory and ventilatory impediment. Objective: The aim of the current study is to evaluate the outcome of percutaneous nephrolithotomy in the free flank modified supine position (FFMSP) regarding the operation duration, hospitalization time, and the effectiveness and safety. Patients and methods: From January 2020 to June 2021, 60 patients (36 males and 24 females) with renal stones underwent PCNL procedure in FFMSP. Descriptive statistics, puncture site, numbers of punctures, operative time, stone free rate, bleeding, modified Clavien grade of complication, re-treatment rate, additional procedures and hospitalization time were presented. Results: Multiple stones were in 53% of the cases, the stone distribution was mainly in the inferior calyces and/or the pelvis of the kidney. Positive history of renal surgery was reported by 70% of cases.  The site of puncture was mainly through the inferior calyx in 83% of cases, 23% of the cases were in need for two punctures, 26% were in need for re-treatment, mean duration of operation was 89.67 (SD 25.2) minutes, mean hospitalization time was 8.3 (SD 6.32) days and the patient's ratio who were free from stones was 86%. The average need for an additional procedure was 20%. The complication grade according to Calvien Dindo classification is mainly grades 2,3A and 4B. Conclusions: The supine position is effective with average operation duration; however, it has a high complication rate, an increased need for additional procedures, a re-treatment rate, a long hospital stay and an increased rate for blood