Although radioiodine is increasingly the treatment of choice in hyperthyroidism, there are regional differences in its use which reflect, in part, concerns regarding safety. We investigated attitudes amongst general practitioners and consultant physicians to the role of radioiodine therapy, and reviewed our own radioiodine prescribing in patients aged less than 40 to elucidate any influence of age and/or sex. We surveyed general practitioners in the former Central Birmingham Health District and consultant physicians in the West Midlands Region to investigate treatment preferences in hyperthyroidism and perceived risk from radioiodine of hypothyroidism, carcinogenesis and infertility. Of 230 general practitioner and 130 consultant physician respondents, less than 1% considered radioiodine the treatment of choice in a 25-year-old female presenting with hyperthyroidism. At relapse after antithyroid drug treatment in a 25-year-old female, only 16.5% of general practitioners and 23.9% of physicians advocated radioiodine, the greatest number preferring partial thyroidectomy. For a 65-year-old at presentation, 49.1% of general practitioners and 62.3% of physicians considered radioiodine the treatment of choice. More than 10% failed to note the risk of hypothyroidism following radioiodine, while 11-34% perceived increased risk of malignancy or infertility. Review of our own practice demonstrated that of 100 patients given radioiodine, 94% were cured of hyperthyroidism when reviewed at a mean of 2.4 years from latest treatment, 70% being hypothyroid. Females given radioiodine were treated less promptly following diagnosis of hyperthyroidism than males (2.2 +/- 0.26 years vs. 1.6 +/- 0.4) and were more likely to have received a preceding course of antithyroid drugs (78% vs. 57%).(ABSTRACT TRUNCATED AT 250 WORDS)