In the framework of the Thyroid initiative Papillon 2001 - 2002 thyroid nodules and sonographically detectable focal lesions with a diameter more than 5 mm were verified in 23.1% of 64.123 persons without a history of thyroid disease. The frequency of such findings was with 33.0% in 46-65 years old persons three times higher then in persons aged 18-30 years (9.6%). In the diagnostic workup thyroid cancer was detected in 15 patients operated on up to now (6 women and 9 men; papillary cancers in 12 cases, follicular cancers in 3 cases) The smallest tumor had a diameter of 1.3 cm, the mean diameter was 2.3 +/- 91 cm. In 3 patients the tumor had invaded the tissue beyond the thyroid capsule, in 4 cases multicentric growth was detected. Lymph node metastases were found in 7/15 cases and distant metastases in 2/15 cases. These result reveal, that thyroid cancer detected by chance may be relatively aggressive. In daily routine, sonographically detectable lesions with poor echogenicity, irregular margins or internal calcifications with a diameter of more than 1 cm should be clarified by fine needle aspiration biopsy.