Objective To compare the safety and efficacy of minimally-access percutaneous nephrolithotomy(Mini-PCNL) in modified lateral position and prone position in high-risk patients with upper urinary tract stones and explore the clinical value of the modified lateral position. Methods We retrospectively analyzed 82 cases of high-risk patients underwent ultrasound-guided percutaneous nephrolithotomy from June 2010 to December 2015. 43 cases in group of modified lateral position and 39 case in group of prone positi...