The purpose of this study was to explore the potential role of power Doppler sonography in guiding percutaneous ethanol injection of autonomously functioning thyroid nodules. Thirty-two patients with pretoxic adenoma and 15 with toxic adenoma underwent percutaneous ethanol injection under power Doppler sonographic guidance. All patients with pretoxic adenoma and 13 of 15 patients with toxic adenoma were treated successfully (normalization of circulating thyroid hormones and thyroid stimulating hormone levels and disappearance of nodular hyperactivity with complete recovery of extranodular tracer uptake at scintigraphy). Power Doppler sonography showed the progressive reduction of the intranodular blood flow until its extinction after 6 to 12 months. Nodular shrinkage was obtained in all patients (from 10.85 +/-1.04 to 2.9 +/- 0.3 ml in pretoxic adenoma and from 15.4 +/- 1.8 to 4.2 +/- 0.7 ml in toxic adenoma. Power Doppler sonographic guidance seems to improve the outcome of percutaneous ethanol injection, allowing detection of blood flow even in very small vessels, permitting the ethanol to be guided toward the main afferent vessels of the nodules, and making it possible to monitor the diffusion and the effects of ethanol on nodular vascularization.