BACKGROUND In recent years percutaneous drainage has been used successfully to treat the hepatic hydatid cysts of echinococcal disease. We performed a controlled trial to compare the safety and efficacy of percutaneous drainage with those of surgical cystectomy, the traditional treatment. METHODS In a prospective study, we randomly assigned 50 patients with hepatic hydatidosis to treatment with percutaneous drainage (25 patients) or cystectomy (25). Albendazole (10 mg per kilogram of body weight per day for eight weeks) was administered to the patients who underwent percutaneous drainage. Serial assessments included clinical and biochemical examinations, ultrasonography, and serologic tests of echinococcal-antibody titers. RESULTS The mean (+/-SD) hospital stay was 4.2+/-1.5 days in the drainage group and 12.7+/-6.5 days in the surgery group (P<0.001). Over a mean follow-up period of 17 months, the mean cyst diameter decreased from 8.0+/-3.0 to 1.4+/-3.5 cm (P<0.001) after percutaneous drainage and from 9.1+/-3.0 to 0.9+/-1.8 cm (P<0.001) after surgery. The final cyst diameter did not differ significantly between the two groups (P=0.20). The cysts disappeared in 22 patients (88 percent) in the drainage group and in 18 (72 percent) in the surgery group (P=0.29). After an initial rise, the echinococcal-antibody titers fell progressively and at the last follow-up were negative (<1:160) in 19 patients (76 percent) in the drainage group and 17 (68 percent) in the surgery group (P=0.74). There were procedure-related complications in 8 patients (32 percent) in the drainage group and 21 (84 percent) in the surgery group, 17 of whom had fever postoperatively (P<0.001). CONCLUSIONS Percutaneous drainage, combined with albendazole therapy, is an effective and safe alternative to surgery for the treatment of uncomplicated hydatid cysts of the liver and requires a shorter hospital stay.