Backgraund/Aim. Conventional cytomorphology of thyroid cell aspirates is limited in preoperative differential diagnosis of follicular adenomas (FA) and hyperplastic adenomatoid nodular goiters from well differentiated thyroid follicular carcinoma (FTC) and follicular variant of thyroid papillary carcinoma (PTC). This is the reason of inaccurate presurgical differential diagnosis and in the same cases of inadequate operative managament. The aim of the study was to evaluate the role of quantitative estimation of thyreocite nuclear features (cariomorphometry) in thyroid aspirated smears in preoperative differential diagnosis of benign from malignant thyroid lesions. Methods. A total of 48 patients with thyroid nodular disease underwent fine needle aspiration biopsy for cytomorphology, cariomorphometric analysis of the aspirates, and histopathologic explorations conducted fully postoperatively. On the basis of cytomorphology classification the patients were divided into three groups: benign (B), n = 8; malignant (M), n = 15, and suspicious for malignancy (S), n = 25. Using a microscope connected to a computerized video system, mean nuclear area, the nuclear area coefficient of variation (NACV) and anisocariosis ratio were measured and calculated. Results. In all the 15 patients with cytologically malignant results the diagnosis of PTC was confirmed histopathologically. All cytologically benign lesions were confirmed histopathologically. Thyroid carcinoma was found in 15 out of 25 patients with suspicious lesions. The highest mean values of nuclear area were in the PCT (90.74 ± 26.71 μm2), and were significantly different from all other groups (p < 0.001). The mean nuclear area in FTC was 69.20 ± 27.31 μm2 and was significantly higher than in the benign adenomatous group (p < 0.01). There was no significant difference in mean nuclear area between FTC and FA, but there was a significant difference in NACV between these two groups (FTC: 39.46 % vs FA: 23.42%, p < 0.001). In 27 out of 30 patients with thyroid carcinoma higher values of NACV than 18% were found. Conclusion. Preoperatively cariomorphometry is a useful method in differential diagnosis of thyroid carcinoma from benign lesions, as a complementary method to convencional cytodiagnostics. The NACV showed highest sensitivity as a parameter of malignant thyroid cell transformation.