This work present the results of the use of 131I, as first line and only, antithyroid treatment, applied to 120 patients suffering from autoimmune hyperthyroidism, compared to 64 patients with toxic goiter and adenoma. The diagnostic weight of the determination of the various antithyroid antibodies was assessed in the identification of autoimmune hyperthyroidism, for which TRAb and TPO Ab are the most significant. The evolution after treatment of a preexisting ophthalmopathy (i.e. Graves'disease) was never found to be alarming and in most cases regularly improved with time. A single case (out of 72) of autoimmune hyperthyroidism with no preexisting sign developed a severe ophthalmopathy after treatment, which was well controlled thereafter. Mean cumulated 131I doses to control hyperthyroidism were 22.8 mCi for toxic goiter, 21.6 mCi for adenoma, 14.1 mCi for autoimmune hyperthyroidism and 16.7 mCi for Graves'disease. Post 131I hypothyroidism was found in 28.2% of toxic goiters, 12.1% of adenomas, 66% of autoimmune hyperthyroidisms and 70% of Graves'disease. No relapse was observed after treatment. A surgical indication was proposed for cases requiring more than two 131I doses to control hyperthyroidism.