OBJECTIVE To study the clinical outcome of treatment of hyperthyroid patients with radioiodine. METHODS Records of patients treated for hyperthyroidism with radioiodine from 1989 to 1992 were examined in 1994, and a questionnaire was sent to patients < or = 70 years with Graves' disease (GD) and toxic nodular goitre (TNG) to obtain information regarding thyroxine substitution, smoking habits and present state of health. METHODS Outpatients in a thyroid unit; follow-up by primary care. METHODS Seven hundred and fifty-four patients with hyperthyroidism treated with radioiodine, 327 receiving the questionnaire, 72% response rate. METHODS Radioiodine treatment using a delivered absorbed dose method, aiming at an absorbed dose to the thyroid of 100-120 Gy. METHODS Statistical analysis of clinical records and results from questionnaire. RESULTS Only 10% of the patients needed more than one treatment. At the time of follow-up, thyroxine supplementation was given to 178 (93%) of the GD and to 21 (47%) of the TNG patients. Smoking was more common in GD patients than in the general population (44% vs. 26%; P < 0.001). Smoking GD patients experienced eye discomfort more often than smoking TNG patients (53% vs. 7%; P < 0.001). Weight gain after therapy was a problem in 79% of the hyperthyroid individuals. CONCLUSIONS Few patients needed retreatment and most of the GD patients had thyroxine after 1-5 years after therapy. Smoking patients, especially those with GD, had more eye symptoms. At follow-up, the euthyroid patients still consider themselves having a poorer health than individuals in the general population.