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Summary

Objective  We aimed to describe the changing incidence of thyroid disease in a population-based study in Tayside, Scotland (population 390 000) between 1994 and 2001.

Design  A retrospective, data-linkage, population-based study measuring the incidence and prevalence of thyroid disease.

Patients  All patients with newly diagnosed, treated and stable thyroid disease in Tayside were identified by electronic linkage of six datasets, including all regional biochemistry data, hospital admissions, deaths and a thyroid follow-up register.

Results  The overall prevalence of thyroid dysfunction has increased from 2·3% to 3·8% (1994–2001). The prevalence of ever having had hyperthyroidism increased from 0·86% to 1·26% in females and 0·17% to 0·24% in males (P < 0·0001 for both). The standardized incidence of hyperthyroidism increased from 0·68 to 0·87 per 1000 females/year, representing a 6·3% annual increase (P < 0·0001). The prevalence of primary hypothyroidism increased from 3·12% to 5·14% in females and 0·51% to 0·88% in males (P < 0·0001 for both). The standardized incidence of primary hypothyroidism did not change and varied between 3·90 and 4·89 per 1000 females/year over the 8 years. Incidence of hypothyroidism in males increased from 0·65 to 1·01 per 1000 males/year (P = 0·0017). Mean age at diagnosis of primary hypothyroidism declined in females from 1994 to 2001.

Conclusions  The prevalence of primary hypothyroidism and previous hyperthyroidism has increased in Tayside, Scotland. This is partly due to an increasing incidence of disease, increased ascertainment and earlier diagnosis of disease. This will result in an increased workload for endocrinologists and general practitioners.