BACKGROUND To evaluate the effectiveness of percutaneous treatment of renal hydatid cysts. METHODS Four male and one female (14-52 years old, mean = 37 years) patients with five renal cysts were treated percutaneously. All five cysts from the patients were pure fluid collections, which were consistent with type I hydatid cysts according to Gharbi's classification. After entering the cystic cavity under sonographic guidance, cystic fluid was aspirated, and the cavity was filled with hypertonic saline (15% NaCl). In three patients with cysts larger than 6 cm in diameter, catheterization was performed under fluoroscopic guidance, and the cavity was filled with 95% absolute alcohol to sclerotize the cyst walls. In two patients with cysts smaller than 6 cm in diameter, the procedure was carried out by a technique in which the cyst was puncture aspirated, hypertonic saline solution was injected, and the cyst was reaspirated. The patients were followed by ultrasonography and computed tomography. Follow up was 5-62 months (mean = 33.8 months). RESULTS Sonographic follow-up examinations indicated a gradual decrease in cyst size and volume. The size reduction was significant (p < 0.05). The volume reduction rate was 55-95% (mean = 81%). During follow up, fluid components of all five cysts reduced gradually and finally disappeared, leaving a remnant that is called a "pseudotumor appearance." Neither mortality nor any dissemination was encountered during follow up. The only complication seen in this series was an abscess that was successfully treated with percutaneous drainage. CONCLUSIONS According to the results of our study, percutaneous treatment of renal hydatid cysts avoids the morbidity of open surgery and preserves the residual function of the kidney.