Percutaneous ethanol injection (PEI) has recently been proposed as an alternative therapy for toxic thyroid adenomas, instead of conventional treatments (pharmacological, surgical and radiometabolic therapies). The aim of this study was to investigate efficacy, complications and prognostic factors of PEI treatment in a group of 74 patients, 14 men and 60 women, treated from May, 1991, to December, 1994. Twenty-seven patients had nontoxic (pre-toxic) nodules (normal T3 and T4 and undetectable TSH serum levels) and 47 toxic nodules (high serum levels of thyroid hormones). A mean of 1.6 ml ethanol/cc of nodule volume was injected in 3-14 sessions (mean = 6). Ten subjects were treated twice, and 2 patients three times. Results were defined as: 1) complete cure: normalization of T3, T4 and TSH levels and appearance of extranodular thyroid tissue at scintigraphy; 2) partial cure: reduction in thyroid hormones within the normal range but still undetectable TSH levels and still suppressed extranodular thyroid tissue at scintigraphy; 3) failure. Complete cure was obtained in 96% of nontoxic (pretoxic) nodules and 65% of toxic ones. Moreover, partial cure was seen in 27.5% more toxic nodules and failure in 7.5%. The most significant complications were a case of transient dysphonia and two cases of common jugular vein thrombosis, both resolved spontaneously. The most important prognostic factor was the degree of hyperthyroidism (as FT4 and T3 serum levels), while nodule volume was rather useless to predict the final result. In conclusion, PEI can be an alternative, effective and low-cost treatment for autonomous thyroid nodules, without any severe complication and well tolerated by the patients.