AIMS: To evaluate all thyroid fine needle aspirations (FNA) done over a six year period to assess the accuracy and value of the technique. METHODS: There were 335 FNAs of which 184 had subsequent histology and 49 others had clinical follow up, providing 233 patients for analysis. All cytology and histology was reviewed with no significant alterations in diagnosis. The FNAs were classified into three groups: benign, suspicious (recommend excision), and malignant. The histology and medical records were reviewed to determine whether the cytology was accurate. RESULTS: There were 130 benign FNAs, 126 had non-malignant histology or normal clinical follow up, and four had malignancies on histology (two lymphomas, one follicular carcinoma, and one carcinoma not otherwise specified). There were 45 suspicious FNAs. Of these five had either follicular or papillary carcinoma, 14 had follicular adenomas, and 26 had colloid nodular goitres or normal clinical follow up. Of the 21 malignant FNAs, 11 had carcinoma and 10 had either a non-malignant histology or normal follow up. There were 126 true negatives, 30 true positives, 4 false negatives, and 36 false positives. This gives a sensitivity of 88%, a specificity of 78%, a positive predictive value of 46%, a negative predictive value of 97%, and an accuracy of 80%. CONCLUSIONS: FNA cytology of the thyroid has a high negative predictive value, which is useful to reassure the majority of patients presenting with thyroid enlargement. However, a negative FNA should never exclude malignancy if there is a strong clinical suspicion. If this rule is adhered to a large number of patients will be spared unnecessary surgery and no malignant nodule will go untreated.