In our centre we use CNB for routine study of thyroid nodules since 2005. Four diagnostic categories for CNBs results have been standardised: insufficient; benign; follicular proliferation (FOL), including follicular and oncocytic neoplasms; and malignant. Diagnosis of FOL was defined according to the presence of microfollicular patterned biopsies with scant or absent colloid, sometimes with minimal pleomorphism or discrete nuclear changes. This category could be equivalent to AUS/FLUS and FN/SFN, III and IV categories in BSRTC, encompassing undetermined diagnosis leading to surgical evaluation. We review surgical results in operated patients. A series of 166 patients (33 men), mean age, 52.8 years (SD 14.5) from 3750 CNBs (207 FOL; 5.5%) all of whom underwent surgery, from October 2005 to December 2014 were retrospectively analysed. They included 102 diagnosed as pure follicular lesions and 64 as oncocytic FOL. The false-positive rate, unnecessary surgery rate, and malignancy rate for the CNB patients according to the final diagnosis following surgery were evaluated. In surgical specimens 32 patients (19.3%) had non-neoplasms (unnecessary surgery), all of which were nodular adenomatous hyperplasia. The remaining 134 nodules were true neoplasms, 31 (18.7%) malignant. Malignant included 16 follicullar carcinomas, 13 papillary carcinomas. one medullary carcinoma and one poor-differentiated thyroid carcinoma. In 23 cases there were incidentally discovered papillary carcinomas (112 mm of size) in the same or contralateral lobe of the biopsied lesion. From 102 adenomas, 17 carried an incidental PTC (16.7%). Globally, there were 54 carcinomas with a CB of FOL (32.5%). CNB shows good/fine precision in diagnosing follicular neoplasms, but as FNA, fail to distinguish adenomas from carcinomas, with a malignancy rate around 20%. We remark the frequent association of benign neoplasm (adenomas) with malignant lesions in the same thyroid (16.7%), supporting surgical treatment when this CB diagnosis is obtained.