Clinical data: a 23-year-old man was referred for an evaluation of a thyroid nodule which had been gradually enlarging for 5 years.

Palpation: a soft nodule in the left lobe.

Functional state: euthyroidism (TSH-level 0.68 mIU/L).

Ultrasonography*: there was a hypoechogenic nodule in or next to the ventral surface of the left lobe.

Cytological diagnosis: suspicion of malignancy - a papillary cancer or an uncommon tumor not of thyroidal origin.

Histopathology: cysta epidermalis in the region of the thyroid.

Comments: we made several mistakes in this case.

1. Malignancy in a soft nodule would be an extremely rare situation.

2. Naturally, we unequivocally misinterpreted the cytological pattern, i.e. necrotic cell groups were misinterpreted as papillary structures.

3. By thorough analysis of sonography, it is clear that the lesion is outside the thyroid.

* The cytological, histological and sonographic pictures, the clinical data in all cases presented in the website belong to the same person. The few exceptions are unequivocally noticed. The patient whose history and cytological, histological photographs are presented in this case history was treated in 1993. The sonographic images are out of date. The sonographic pattern was identical to that described above, but the sonographic pictures were replaced with those of another patient with histologically proven epidermoid cyst. We think that one can learn from our mistakes, that is why we used these pictures.