BACKGROUND: Percutaneous ethanol injection(PEI) performed in guidance of ultrasonography has been used in cases of thyroid cyst and autonomous functiong thyroid nodule(AFTN). We performed this study to determine the feasibility of PEI on the various type of benign cold nodules(solid, pure cyst, complex cyst) and AFTN. METHOD: Ninety patients(age 41+12 years; 83 women and 7 men) with hot and cold nodule were included in this study. All cases were subjected to FNAB, and sono-guided in cases of complex cyst, at least twice with results of colloid nodule. T4 suppression treatment was done for cold solid nodules for at least 6 months and cases which had partial response(50% or more volume reduction but no further volume decrease on T4 suppression) were included in this study. After PEI, we classified AFTN into three different response groups; complete response (normali- zation of TFT and thyroid scan finding), partial response(normalized freeT4 but suppressed TSH or persistently suppressed scan), or failure group. Each subtypes(solid, pure cyst, complex cyst) of cold nodules were also classified into three groups in accordance with volume reduction; complete response(above 90% of volume reduction), partial response(50-90%), and failure(below 50% or increase in size) group. RESULTS: Overall responses rate of PEI for benign thyroid nodule were complete; 70(78%), partial; 18(20%), and failure; 2(2%). In 27 cold solid nodules, complete response was observed in 23(85%) and partial response in 4(15%). In 11 pure cysts, complete response was observed in 7(64%), partial response in 3(27%), and 1 case(9%) of failure was lost after 1 trial of PEI. In 45 cases of complex cyst, complete response was observed in 36(80%), partial response in 8 (18%), and 1 case(2%) of failure was subjected to operation with pathology report of Hiirthle cell adenoma. In 7 cases of AFTN, complete response was observed in 4(57%) and partial response in 3(43%). We observed complications during PEI therapy such as transient neck pain(n=10), transient unilateral vocal cord palsy(n=l), and intracavitary hemorrhage(n=2), transient hypotension during ethanol injection(n 1). CONCLUSION: Our data suggest that efficacy of PEI(57%) in AFTN is inferior to conventional therapies like surgery and radioiodine, but still can be an alternative therapeutic modality in selected cases. In cold nodules, especially of solid type and complex cyst, PEI may have feasibility as a therapeutic modality in restricted cases. Further studies of prolonged follow-up for the possibility of neglecting occult malignancy are warranted.