In papillary thyroid carcinoma (PTC) in cytological and surgical specimens, fine chromatin, nuclear grooves and nuclear pseudoinclusions are the hallmarks of diagnosis. We investigated the significance of these nuclear changes in neoplastic non-PTC lesions. Fine needle aspiration biopsies (FNAB) of thyroid lesions were reviewed with histologic correlation. Twenty-five low-grade PTC and 35 neoplastic non-PTC lesions with a fine chromatin pattern in cytology specimens were identified. These lesions were studied along with five multinodular goiters and five follicular adenomas with a coarse chromatin pattern. The neoplastic non-PTC lesions were selected from cases with a histopathologic diagnosis of follicular neoplasm (accompanied by cytopathologic examination) but lacking a coarse chromatin pattern. The nuclear changes were separated into three grades of nuclear atypia with a fine chromatin pattern, depending on the degree of nuclear enlargement and nuclear membrane thickening, or the presence of nuclear grooves or pseudoinclusions. Thyroid lesions with a higher grade of nuclear atypia with a fine chromatin pattern were associated with larger nuclei and more readily visible nucleoli. These lesions correlated histologically with PTC and follicular adenomas with a fine chromatin pattern. The latter could be divided into three grades: grade 1 lesions having a fine chromatin pattern similar to that of nuclei with open chromatin seen in areas of nodular goiter; grade 3 lesions having nuclear features closest to those of PTC; and grade 2 lesions showing intermediate changes. In conclusion, there is a spectrum of nuclear changes in neoplastic non-PTC lesions with a fine chromatin pattern. These lesions are often diagnosed as follicular adenomas in surgical pathology and pose cytopathologic diagnostic problems between nodular goiter, follicular adenoma and PTC. The significance of follicular adenomas with a fine chromatin pattern will be discussed.