Objective: Little is known about the long-term effects of Graves' opthalmopathy (GO) on health-related quality of life (HRQL) after the eye treatment is considered to be finished. The aim of this study was to quantity these effects using validated HRQL questionnaires. Design: A cross-sectional follow-up study was carried out in GO patients who had started radiotherapy and/or prednisone treatment between 1982 and 1992. Methods: Between 1998 and 2000 these patients received an HRQL questionnaire containing the SF-36, EuroQol and GO-QOL questionnaires. All patients were invited for a follow-up ophthalmological examination. HRQL scores of the respondents were compared with those of two reference populations of 'healthy' persons and to scores of several other GO populations. Results: One hundred and sixty-eight patients were included; 163 completed the HRQL questionnaire and 154 visited the outpatient clinic. The median follow-up was 11.7 years. A considerable number of symptoms related to GO were found. More than half of the patients had diplopia and 28% had a low visual acuity. Sixty per cent had a proptosis of at least 20 mm. The HRQL scores were considerably better than those of newly diagnosed GO patients (untreated) and GO patients who completed the questionnaire during treatment, but worse than those of 'healthy' persons. Although we did not perform a longitudinal study, we included a selected group of patients who had been treated with radiotherapy and/or prednisone in the Academic Medical Centre of the University of Amsterdam, and though we could not assess HRQL at comparable times after receiving treatment, this is the first study that presents any data on the long-term effects of GO on HRQL. Conclusion: GO has a marked negative effect on HRQL, even many years after treatment. These findings suggest that GO should be considered a chronic disease. Aftercare is needed for these patients after their immunosuppressive and surgical treatments.