Comparing prone to modified supine percutaneous nephrolithotomy – a single surgeon experience. Introduction Percutaneous Nephrolithotomy (PCNL) is traditionally performed in the prone position. This has significant anaesthetic ramifications and is time consuming. A modified supine PCNL has been described, which is a technique that has many anaesthetic 1 and operative benefits. These include the ability to simultaneously treat ureteric calculi, thereby avoiding additional procedures; decreased manual handling of the patient and decreased operating time 2. Despite these benefits, it is not common practice in Australia due to lack of training and fear of complications. Conclusions Despite only recently being introduced to our unit, the results of the modified supine PCNL have been equivalent to the previous prone cases with a significant reduction in operating time. This is despite the increasing stone complexity and increased BMI in the supine series. Most of this reduction will be due to the avoidance of repositioning, though other advantages have included gravity induced stone expulsion and simultaneous ureteric stone treatment. We strongly feel that the modified supine position is superior to the prone and should now be used routinely for all large renal/proximal ureteric stones. Results Groups were well matched for age. 3 of the supine group were not considered fit enough for prone procedures due to morbid obesity and pre-existing chest problems. Operating time for the supine group was significantly shorter than for the prone group (median time 86 minutes v 116 minutes, range v ). Complications were similar in both groups with no significant difference between the two. One patient from the supine group was converted to prone after an unsuccessful puncture. This was the 5 th patient in the supine series, and was considered to be part of our learning curve. Methods  41 consecutive modified supine PCNLs were performed between April 2011 and March  41 operations were performed on 36 patients (5 patients had re-PCNL) with large renal calculi or ureteric calculi >2cm.  A single Consultant surgeon was involved, with 7 different trainees performing punctures (3 registrars and 4 fellows) These were his first 41 PCNLs performed in a supine position. Data for the supine cohort was collected prospectively All patients were followed up with X-ray or CT KUB Stones were fragmented using either a lithoclast or ultrasonic lithotripter. For complex staghorn calculi, a second surgeon performed simultaneous ureterorenoscopy using the Holmium:YAG laser for fragmentation. The patient demographics, stone size, operating time and clearance rates were compared to the immediate previous 41 prone cases (36 patients) and analysed statistically. Aim We have recently changed from offering routine prone position for PCNL to a modified supine technique. We have compared our first 41 modified supine cases with the previous 41 prone cases. References 1 Atkinson C, Turney B, Noble J, Reynard J, Stoneham M. Supine vs Prone Percutaneous Nephrolithotomy: An anesthetist's view. BJUI. 2011; Aug; 108(3) Wu P, Wang L, Wang K. Supine versus prone position in percutaneous nephrolithotomy for kidney calculi: a meta-analysis. Int Urol Nephrol. 2011; 43:67-77 K. Rzetelski-West, Jacob Gleeson, Phil McCahy Department of Urology, Casey Hospital, Berwick, Victoria Poster presentation sponsor No. 046 CharacteristicsProneSupineP value Age (years) Median: Range: p=0.954 Male:Female15:2626:15 Body Mass Index (BMI) p=0.067 Operating time (minutes) Median: Range: p= 0.003* Stone Size (mm) p=0.0402* Additional ureteric calculi07 Length of Stay (days)2.5 p=0.9136