Evaluation of the frequency of Graves' ophthalmopathy (GO) and its management in children and adolescents up to 18 years old with Graves' hyperthyroidism. This was a questionnaire study (QS) among members of the European Thyroid Association and the European Society for Paediatric Endocrinology. Approximately 300 QS were sent to members with electronic addresses and 110 QS were returned from 25 countries: 52 respondents said they had no experience with Graves' disease in this age group, but 67 respondents (23 paediatric and 44 adult endocrinologists) completed the QS. Out of 1963 patients with juvenile Graves' hyperthyroidism seen by respondents in the last 10 years, 641 (33%) had GO; about one-third of GO cases were < or =10 years old, and two-thirds were 11-18 years old. The prevalences of GO among juvenile Graves' hyperthyroidism were 36.6, 27.3 and 25.9% in countries in which the smoking prevalence among teenagers was > or =25, 20-25 and <20% respectively (P < 0.0001 by chi(2) test). When confronted with the standard case of a 13-year-old girl with Graves' hyperthyroidism and moderately severe active GO, the diagnostic approach included on average 4.9 biochemical tests (TSH, free thyroxine (FT(4)) and TSH.R-Ab, 100-88% of respondents) and 2.4 specific investigations (thyroid ultrasound by 69%, orthopsy/visual fields/visual acuity by 64% and orbital magnetic resonance imaging or computed tomography by 63%). Antithyroid drugs were the treatment of choice for 94% of respondents; 70% recommended a wait-and-see policy and 28% corticosteroids for the co-existing GO. In variants of the standard case, a younger age did not affect therapeutic approach very much. Recurrent hyperthyroidism would still be treated with antithyroid drugs by 66%, and with (131)I by 25%. Worsening of GO or active GO when euthyroid would convince about two-thirds of respondents to initiate treatment of GO, preferably with steroids. GO occurs in 33% of patients with juvenile Graves' hyperthyroidism; its prevalence is higher in countries with a higher prevalence of smoking among teenagers. The diagnostic approach to the standard case of a 13-year-old with Graves' hyperthyroidism and moderately severe active GO involves on average five biochemical tests; thyroid as well as orbital imaging is done in 84% of cases. Antithyroid drugs remain the treatment of choice for 94% of respondents, and even so in case of recurrences (66%). For GO, 70% recommend a wait-and-see policy; intervention, preferably with steroids, is advocated by two-thirds of respondents in cases of worsening or still-active eye disease despite euthyroidism.