There have been many encouraging studies on medical treatment of pulmonary hydatid disease due to Echinococcus granulosus infection. Our aims were to demonstrate the safety and efficacy of medical treatment in pulmonary hydatid disease and to describe a pediatric population who would benefit from medical treatment, especially in respect to the diameter of the hydatid cyst. All patients were treated with mebendazole or albendazole. Treatment outcome was defined as cure, improvement or failure. Among 82 patients, 34.1% were cured, 34.1% improved and 31.8% failed. When 102 cysts were individually evaluated, 36.31% were cured, 32.4% improved and 31.3% failed. The cure and the failure rates were statistically insignificant in cysts treated with mebendazole and albendazole; however statistically significantly more cysts were improved with albendazole. The results were statistically insignificant between continuous and cyclic albendazole treatment. The mean size of successfully treated cysts was 5.3 +/- 3.4 cm, but "failed' for cyst with a mean size of 7.3 +/- 4.3 cm. There was a positive, weak and statistically significant correlation between the cyst size and treatment results. The major complication was infection. We suggest that selected pediatric patients with uncomplicated pulmonary hydatid cysts sized less than 5 cm should have a trial of medical treatment with a very close follow up. (c) 2005 Elsevier Ireland Ltd. All rights reserved.