From 1985 to 1991 there were 5889 fine-needle aspiration biopsies of thyroid performed in our laboratory. 703 cytological diagnoses based on biopsy specimens taken from 679 patients, were compared with the results of postoperative histopathological examinations. There were 14% non-diagnostic biopsies. The statistical analysis was performed considering difficulties in differentiation between follicular adenomas and follicular carcinomas. Difficulties in evaluation of biopsies of cystic lesions were also considered. The results of cytological and histopathological examinations were agreeing with one another in 88% cases. In regard to diagnosis of malignant neoplasms, the sensitivity of the cytological investigation was equal to 63% and the specificity equaled to 90%. While considering detection of papillary carcinomas, the sensitivity was equal to 67%. Our results are in a compliance with the view, that the fine-needle aspiration biopsy is a useful method in a preoperative diagnosis of thyroid lesions.