Six patients with Baker's cysts, 3 with branchial cleft cysts, and 2 with thyroglossal duct cysts were treated with percutaneous aspiration and absolute ethanol sclerotherapy using a 7-French pigtail catheter. Cystography was performed before ethanol injection to confirm that there was no extravasation and that it was a monocystic lesion. One recurrence of a Baker's cyst was revealed in follow-up examinations, which ranged from 11 months to 36 months (mean, 25 months). The major complication of hypoesthesia of the popliteal region was observed in 1 patient treated for Baker's cyst. The results of this series suggest that ethanol sclerotherapy is the treatment of choice for Baker's cyst, branchial cleft cyst, and thyroglossal duct cyst.