Interinstitutional consultation in pathology has shown to improve patient safety by detecting interpretive errors that may significantly impact clinical management. We conducted a study of 922 cases of thyroid FNAC slides, referred to our institution over a 2-year period, to assess the magnitude of discrepancies and determine the clinical impact of second opinion. Disagreements were categorized as none, minor or major, the latter two defined as one- or two-step deviations respectively on the NCI diagnostic categories scale. There were 122 disagreements (13%), including 44 major and 78 minor. Seventy-five patients underwent a change in management based on second opinion, in conjunction with clinical and radiologic findings (age, size of nodule, family history, ultrasonographic appearance, and solitary versus multiple nodules). The second opinion was supported on follow-up in 57% of major discrepancies, and the initial diagnosis was concurrent with the surgical diagnosis in 7% cases. The remainder (36%) of major discrepancy cases did not undergo surgery, precluding tissue confirmation. Critics have alleged increased costs due to interinstitutional consultations. However, cost avoidance from lost wages, potential surgical complications, and litigation is not easily quantified. Using a simplified calculation to objectively measure the costs associated with changed diagnoses, we estimate that second opinion of these 922 cases resulted in potential cost saving of $940,166 based on current Medicare reimbursement codes. Our study indicates the need for a quality-control program of outside thyroid FNA slides, especially in “high discrepancy categories” as discussed in the article. Diagn. Cytopathol. 2011;. © 2011 Wiley-Liss, Inc.