PATIENTS AND METHODS The result of radioiodine treatment administered to 126 patients with hyperthyroidism between 1986 and 1991 were analysed retrospectively. The indications for radioiodine treatment were single hyperfunctioning nodules (n = 47), multinodular goitre (n = 33), diffuse goitre (n = 19) and Graves' disease (n = 27); the respective doses of 131I, calculated with the Doering and Kramer formula, were 300 Gy (30,000 rad), 150 to 200 Gy (15,000 to 20,000 rad), 100 to 120 Gy (100,000 to 120,000 rad) and 100 Gy (100,000 rad). The uptake of radioiodine was measured on a daily basis and in the case of 46 patients (36.5%) additional treatment given on the third day of treatment. RESULTS For the patients undergoing regular follow-up, data were collected in 1992, at least six months post-therapy. Evaluation revealed a total applied dose of 131I of 20 +/- 12.4 mCi (median +/- SD) per patient. non-response to treatment making hospitalisation and renewed therapy necessary was observed in 1.6% of the group. In only two further patients did scintigraphy reveal compensated toxic adenoma. In 36% of patients with single hyperfunctioning nodules, 21% of those with multinodular goitre, 53% of those with diffuse goitre and 56% of those with Graves' disease hyperthyroidism was observed. In the great majority of cases, hypothyroidism occurred in the first year following treatment.