A survey has been conducted in Whickham, County Durham, to determine the prevalence of thyroid disorders in the community. Two thousand seven hundred and seventy-nine people (82.4% of the available sample) were seen in the survey. The prevalence of overt hyperthyroidism was 19/1000 females rising to 27/1000 females when possible cases were included, compared with 1.6–2.3/1000 males. The prevalence of overt hyothyroidism was 14/1000 females rising to 19/1000 females when possible cases were included, compared with less than 1/1000 males. The prevalence of spontaneous overt hypothyroidism (excluding iatrogenic cases) was 10/1000 females or 15/1000 females including unconfirmed cases. Minor degrees of hypothyroidism were defined on the basis of elevated serum thyrotrophin (TSH) levels in the absence of obvious clinical features of hypothyroidism. TSH levels did not vary with age in males but increased markedly in females after the age of 45 years. The rise of TSH with age in females was virtually abolished when persons with thyroid antibodies were excluded from the sample. TSH levels above 6 mu/1 were shown to reflect a significant lowering of circulating thyroxine levels and showed a strong association with thyroid antibodies in both sexes, independent of age. Elevated TSH levels (>6mu/l) were recorded in 7.5% of females and 2.8% of males of all ages. Thyroglobulin antibodies were present in 2% of the sample. Thyroid cytoplasmic antibodies were present in 6.8% of the sample (females 10.3%, males 2.7%) and their frequency did not vary significantly with age in males but increased markedly in females over 45 years of age. 3% of the sample (females 5.1%, males 1.1%) had thyroid antibodies and elevated TSH levels and the relative risk of a high TSH level in subjects with antibodies was 20:1 for males and 13:1 for females, independent of age. Small goitres (palpable but not visible) were found in 8.6% of the sample and obvious goitres (palpable and visible) in 6.9%. Goitres were four times more common in females than in males and were most commonly found in younger rather than older females. TSH levels were slightly but not significantly lower in those with goitre than in those without goitre. There was a weak association between goitre and antibodies in females but not males.