Percutaneous puncture followed by instillation with 10% povidone iodine was performed on 23 patients with benign renal cysts. All patients showed remarkable reduction (mean: 86.6%) in size of renal cyst on sonography or computed tomography within a short time (mean: 143 days). Twelve (85.7%) of the 14 symptomatic patients due to the disease were relieved of subjective symptoms such as lumbago after instillation. In a 71 year-old man, microscopic hematuria disappeared after this treatment. There were no complications with this treatment except in one patient who suffered from perinephritis due to a technical problem. This treatment seems to be a safe and effective way to prevent recurrence of cystic fluid.