We observed a general increase in the prevalence of diagnosed PHPT in Tayside, Scotland. The incidence of diagnosis is greater in females than in males and increases with age. The annual incidence followed an apparent cyclic curve during the study period.

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.

The use of these age-specific reference intervals for TSH, especially in those over 70 years old, would result in the reclassification of many TSH results from "abnormal" to "normal" (within the 95th centile reference interval) and avoid unnecessary treatment.

Sex-linked genes may account for the intrinsic sex difference observed. These genes may have an important impact on the development of insulin resistance and the metabolic syndrome and may help to explain the female preponderance of type 2 diabetes in children. Their identification may also help in understanding the pathogenesis of insulin resistance.

Mortality and morbidity were increased for patients with mild untreated PHPT, which is similar to more severe PHPT.