We sent out a questionnaire to 112 women treated for diffuse toxic goitre 2-5 years earlier to evaluate the prevalence of problems with overweight after the disease. Of 87 responders, about 50% (irrespective of surgical or radioiodine treatment) reported weight problems, and we randomly selected 40 of these women (20 with and 20 without reported weight problems) for a clinical follow-up (32 appearing). At the follow-up examination (mean 4 years after treatment for hyperthyroidism), 27 women had a higher weight than their estimated premorbid weight. The weight gain correlated with the estimated premorbid body mass index (BMI; P < 0.005), indicating that excess weight gainers may have had a premorbid problem now exaggerated in the post-hyperthyroid period. However, many women with a BMI within the limits stated to be ideal (21-25 kg/m2) also showed dramatic increases in weight. In contrast, the average middle-aged woman in our region did not appear to have gained in weight during a corresponding time period as judged from a longitudinal population study. Women with reported weight problems (mean weight increase 15.6%, n = 16) did not differ from women without (mean weight increase 6.7%, n = 16) as regards pretreatment hormone levels, method of treatment, (change of) smoking habits or post-treatment levothyroxine administration, or in serum concentrations of thyroid hormones, thyrotrophin, cortisol, procollagen-III-peptide, cholesterol, HDL cholesterol or triglycerides. Women with hyperthyroidism should be informed about the risk of gaining weight after therapy and given early support as to dietary and lifestyle change.