Clinical data: a 17-year-old girl was referred for an evaluation of a newly discovered thyroid nodule. A solitary firm nodule was palpable in the right lobe.

Hormonal investigation: indicated euthyroidism with TSH 0.88 mIU/L.

Ultrasonography revealed a solitary hypoechogenic nodule with increased intranodular flow.

Cytology resulted in benign follicular proliferation.

Surgery was performed because of the size of the nodule.

Histopathology: papillary cancer.

Comment. It was one of our false negative cytological diagnosis caused by error of microscopical interpretation. We overlooked the presence of inclusions.