Objective To evaluate the efficacy of closed retroperitoneoscopic decortication of renal cysts.Methods Closed retroperitoneoscopic decortication of renal cysts was performed in 11 cases from December 1996 to September 2003 in this hospital.A 1~2 cm skin incision 2 cm above the iliac crest was made in the middle axillary line.A 10 mm trocar was introduced into the retroperitoneal cavity.A self-made water-filled balloon was used to create a retroperitoneal space for clearing the renal cyst.An electrocautery scalpel was used to excise the cyst wall until 0.5~1.0 cm away from the renal parenchyma.Results The procedure was successfully completed in 10 cases,with an operation time of 30~100 min(mean,77.5 min) and an intraoperative hemorrhage volume of 20~60 ml(mean,30.9 ml).A conversion to open surgery was required in 1 case because of difficult exposure of the renal cyst.Peritoneal injury was encountered in 1 case.The length of postoperative hospital stay was 6~9 days(mean,7.4 days).(Follow-up) observations in 7 cases for 7~26 months(mean,15.2 months) showed no recurrence of renal cyst under ultrasonography.Conclusions Closed retroperitoneoscopic decortication of renal cysts is a surgical option with little invasion,quick recovery,and good efficacy.