Routine interinstitution pathology consultation can result in change in pathologic diagnosis in up to 10% of patients. In this study, we compared the outside cytopathologic diagnosis of thyroid fine-needle aspiration (FNA) specimens with the in-house diagnosis at the University of Pennsylvania Medical Center over an 18-mo period and its effect on patient management. One hundred ten (60%) diagnostic disagreements were identified among 183 patients. In 16 cases, the diagnosis was changed from benign to malignant, and in 12, the diagnosis was reversed from neoplastic/malignant to benign. Histologic follow-up was available in 109 cases; the overall accuracy of outside diagnosis was 73%, and that of inside diagnosis was 85%. In conclusion, we strongly recommend interinstitution cytology consultation on referred thyroid FNA cases, since our data showed a significant change in diagnosis, thus affecting patient management. Diagn. Cytopathol. 25:231–234, 2001. © 2001 Wiley-Liss, Inc.