PURPOSE: Percutaneous ethanol injection therapy has been used in the treatment of the benign thyroid diseases. Although the reported side-effects of the therapy was mild and transient, some side-effects including local or radiating pain are troublesome to the patients. Radioactive iodine also has been effectively and safely used for management of the benign thyroid diseases. So we developed the percutaneous intranodular injection therapy of radioactive iodine as an alternative of percutaneous ethanol injection therapy. METHODS: From December 1998 to October 1999, we treated 29 outpatients (25 women and 4 men, mean age: 47±12 years). Inclusion criteria were follows; age > 30 years, cytologically benign, with normal thyroid function, cold nodule on thyroid scintigram, solid or mixed natured nodules in sonographical evaluation. Nodular volume was estimated by sonography according to the ellipsoid formula. Radioactive iodine (0.1 mCi/ml) was administered in a single dose injection. Follow-up studies every 3 months consisted of full history, thyroid function test, and sonography. We determined the therapeutic response is effective if the volume reduction of the nodule occurred above 30%. ESULTS: RAfter at least 3 months follow-up, 11 patients showed effective response, 12 patients showed minimal or unchanged response and 6 patients showed progression. Although side-effects such as injection pain, febrile reaction, and hormonal changes were absent, an infectious complication in injection site was developed from 1 case. CONCLUSION: Although we need a more prolonged follow-up to evaluate the delayed sequelae, we can suggest that percutaneous intranodular injection therapy of radioiodine may be an attractive non-surgical treatment in selected cases of benign thyroid nodules.