Background: There is no information about the prevalence of thyroidal diseases in the general Chilean population. Aim: To assess the prevalence of thyroidal diseases in individuals attended in occupational health examinations. Subjects and methods: Four hundred seventy two individuals were examined between 1998 and 1999. In all, serum levels of thyroid hormones, TSH and anti thyroidal antibodies (anti microsomal, anti thyroid peroxidase and anti thyroglobulin) were measured. Results: Forty four subjects were excluded from the study due to an incomplete medical record and 18 due to a personal history of thyroidal disease. Abnormal serum levels of thyroid hormones or TSH were detected in 28 subjects (6.8%). Four (1%) had hypothyroidism, 23 a subclinical hypothyroidism (5.6%) and one (0.2%) had hyperthyroidism. In 87 subjects (21.2%) at least one of the antibodies was positive. Positive anti thyroid antibodies were found in 14 of 28 subjects (50%) with abnormal thyroid hormone levels, compared with 73 of 382 subjects (19.1%) with normal thyroid hormone levels. Thyroid dysfunction was twice as frequent in women than in men. Conclusions: In this sample, a 6.8% prevalence of abnormal thyroid function tests was detected. (Rev Méd Chile 2001; 129: 155-60).