This study aimed to estimate prevalence of thyroid disorders in the São Paulo Ageing & Health Study, an epidemiological study addressing several health-adverse outcomes among elderly people living in a poor area of São Paulo, Brazil. All participants answered a questionnaire and had a blood sample collected to assess levels of thyrotropic hormone and free-thyroxine. Among 1,373 people (60.8% women), prevalence rates (95% confidence interval) for thyroid dysfunction (%) were: overt hyperthyroidism, 0.7% (0.2-1.1)[women: 0.8% (0.2-1.5); men: 0.4% (0.01-0.9)]; overt hypothyroidism, 5.7% (4.5-6.9) [women: 5.9% (4.3-7.5); men: 5.4% (3.5-7.3)]; subclinical hyperthyroidism, 2.4% (1.6-3.2) [women: 2.8% (1.6-3.9); men: 1.9% (0.7-3.0)]; and subclinical hypothyroidism, 6.5% (5.2-7.8) [women: 6.7% (5.0-8.4); men: 6.1% (4.1-8.2)]. There was no difference in prevalence rates according to gender, but almost 40% of women were diagnosed and under treatment compared to 9% of men. The burden of thyroid disorders in this sample is high and most participants were not aware of them.