High-frequency ultrasound examination of the thyroid was performed in 253 subjects (130 women and 123 men; age range, 19-50 years) that were randomly selected from the population in an area of Finland where goiter is not endemic. Thyroid echo abnormalities were detected in 69 subjects (27.3%). Prevalence of abnormalities increased with age, and women showed more lesions than did men in each of the 3 decades. The abnormality was solitary in 39 subjects (57%), multiple in 15 (22%), and diffuse in 15 (22%). Of the 68 individual nodules, 48 (70%) were smaller than 1 cm in diameter. Anechoic rounded nodules 1-5 mm in diameter were found in 28 subjects. Fine-needle aspiration biopsy was performed in 30 subjects. Cytologic examination revealed no unequivocal malignancies. In eight subjects (3.2%) with a diffuse echo abnormality, cytologic evaluation indicated lymphocytic thyroiditis. It is concluded that the prevalence of small thyroid echo abnormalities in a randomly selected adult population is rather high, a fact that supports use of a conservative approach to these types of findings.