[en] To evaluate the efficacy and safety of sono-guided ethanol sclerotherapy for benign thyroid cysts. We studied 22 patients with benign thyroid cysts (9 pure and 13 complex) confirmed by fine needle aspiration biopsy. The procedure was performed every one or three months for a total of one or two sessions (mean 1.2 times). Sono-guided needle aspiration of the cysts was followed by instillation of absolute ethanol (99.9%) into the cystic cavity ; the injected volume of ethanol was 40-100% that of aspirated fluid. Follow-up ultrasonography was performed one to ten months (mean : 3.5 months) after the final session, and complications occurring after ethanol sclerotherapy were observed. Initial cystic volume was 3.5-42(mean : 13)ml. In 21 patients(95%), cystic volume had decreased : In 13 patients(59%), the decrease was 50% or more, and in six (27%) was 1-49%. In two patients(9%), the cysts had been obliterated, but in one there was no change. The volume of instilled ethanol correlated significantly with the volume reduction rate of the cyst (p < 0.01, t test). After ethanol sclerotherapy, the volume of thyroid cysts larger than 10ml had significantly decreased compared to that of thyroid cysts with a volume less than 10ml (p < 0.005, t test). Important longstanding and severe complications were not observed ; in two patients, a small amount of leakage in subcutaneous tissue caused local pain and redness. Sono-guided ethanol sclerotherapy is a safe and effective tool for the treatment of benign thyroid cysts