Fine needle aspiration cytology of "cold" nodules of the thyroid has proved to be of great value in their preoperative diagnosis. Most types of thyroid tumors are readily recognizable from characteristic cellular patterns in the smears of needle aspirates. But follicular neoplasms present some problems because the cytomorphology of the adenomas frequently is same as in carcinoma. For differentiation of benign from malignant follicular neoplasms of the thyroid we tested the usefulness of two objective parameters - nuclear area and perimeter - by morphometry. This study was made on fine needle aspirates from 30 cases with cytologic diagnosis of follicular neoplasm of thyroid. The histologic classification was follicular adenoma in 22 cases and follicular carcinoma in 8 cases. As a reference group we used seven caes with nodular hyperplasia. The smears of aspirates were stained by Papanicolaou method. On each slide 200 randomly selected cells with intact nuclei were measured. The mean value of nuclear area are $25.32{pm}5.50{mu}m^2,;34.08{pm}7.50{mu}m^2;and;39.97{pm}6.63{mu}m^2$ in nodular hyperplasia, follicular adenoma, and follicular carcinoma, respectively. The mean value of perimeter are $19.48{pm}2.26{mu}m,;22.95{pm}2.65{mu}m;and;24.78{pm}2.23{mu}m$ in nodular hyperplasia, follicular adenoma and follicular carcinoma, respectively. The mean nuclear areas and perimeters of cells from follicular adenoma were significantly larger than those from nodular hyperplasia (p<0.05). The mean nuclear areas and perimeters of cells from follicular carcinoma were larger than those from follicular adenoma but the differences are not significant statistically(p>0.05). Therefore, morphometric assessment alone is inadequate to predict malignancy in thyroid aspirates.