Follicular cell predominance in the cytologic examination of dominant thyroid nodules indicates a sixty percent incidence of neoplasia. The interpretation of aspiration cytologic smears that contain a predominance of follicular components often presents a dilemma to the clinician who is treating a patient who has a dominant thyroid nodule, especially when thyroid-stimulating hormone suppression does not produce any significant involution of the dominant nodule. We reviewed a consecutive series of 555 fine-needle aspiration cytologic examinations of dominant thyroid nodules. All specimens that contained colloid or follicular cells mixed with lymphocytes or Hurthle cells were excluded from this review. Additionally, nine aspirates contained degenerated follicular cells with insufficient material for cytologic diagnosis. The remaining 76 specimens contained a predominance of follicular cells: 27 specimens were interpreted as containing "normal" follicular cells, and the remaining 49 specimens were read as "atypical" follicular cells. Histopathologic examination of the resected specimens indicated a 60% incidence of neoplasia (30% carcinoma, 30% adenoma) in which the aspiration cytologic study was interpreted as "normal" follicular cells. On the other hand, a 63% incidence of neoplasia (27% carcinoma, 36% adenoma) occurred in which the cytologic study was read as "atypical." In conclusion, aspirates showing a predominance of follicular cells, whether "normal" or "atypical" indicate a 60% incidence of neoplasia in dominant thyroid nodules that do not decrease significantly in size with thyroid-stimulating hormone suppression. 