OBJECTIVE To evaluate percutaneous single-session sclerotherapy with ethanol without drainage of the sclerosing agent in symptomatic simple renal cysts that require treatment. METHODS A prospective series of 30 consecutive patients with symptomatic simple renal cysts with volume of 280.3 +/- 365.23 mL (range 28-1700 mL) estimated by ultrasonography were treated between July 1999 and July 2003. The cysts were punctured with an 18-gauge, 20-cm needle under ultrasound guidance and local anesthesia. A volume of ethanol equivalent to one third of the aspirated volume, up to a maximum of 100 mL, was injected into the cyst and left there. The patients were reassessed at 1, 3, and 6 months. RESULTS The procedure was technically feasible in all patients. The aspirated volume was 259.8 +/- 265.2 mL (range 30-1900 mL). After 1, 3, and 6 months, the average volume was 52.7 +/- 71.4 mL, 22.7 +/- 43.2 mL, and 11.6 +/- 30.7 mL, respectively. After this period, 28 patients (93%) were asymptomatic, showing total remission of the cyst (17 cases) or at least a 90% decrease (10 cases) or a 50% decrease (1 case) in the initial volume. One patient (3%) had a 50% reduction of the cyst and persistent symptoms, and one patient (3%) had persisting symptoms despite the total remission of the cyst. CONCLUSIONS Single-session percutaneous sclerotherapy with ethanol is a good option for the treatment of symptomatic renal cysts, as it is highly effective and offers the benefits of a less-invasive procedure.