Table 2. Bethesda System for Reporting Thyroid Cytopathology 21.

Bethesda category	Risk of malignancy	Comment
I – Non-diagnostic	5–10%	Insufficient sample of follicular cells or sample has degraded
II – Benign	0–3%
III – Atypia of undetermined significance or follicular lesion of undetermined significance	10–30%	Categories III and IV reflect the inherent limitations of cytology – being unable to distinguish between benign versus malignant follicular patterned lesions given the inability to analyse the tissue architecture
IV – Follicular neoplasm or suspicious of a follicular neoplasm	25–40%
V – Suspicious of malignancy	50–75%	Subtle or focal features of malignancy within the sample
VI – Malignant	97–99%