Fine-needle aspiration cytology (FNAC) is a diagnostic tool used in the clinical workup of solitary thyroid nodules; however, differential cytologic diagnosis of these nodules often is challenging. With the goal of identifying cytologic findings that could improve predictions regarding the presence of neoplastic lesions, the authors performed a retrospective review of cases in which FNAC led to diagnoses of solitary cellular nodules or cellular microfollicular lesions at two university hospitals. FNAC smears associated with cases for which surgical specimens subsequently were obtained were reviewed. FNAC accurately detected follicular neoplasms in 76% of cases at one hospital and in 67% of cases at the other. In the current report, the cytologic findings made in these cases are reevaluated, and the potential diagnostic contribution of available clinical data is discussed. (C) 2004 American Cancer Society.