['FUNDAMENTALS AND OBJECTIVES: Frozen section (FS) constitutes a diagnostic procedure in patients following hemithyroidectomy. It is used to diagnose malignant lesions and to avoid reoperations. Our objective is to confirm this test as useless to rule out cancer.', 'Retrospective and comparative trial between two series of patients following hemithyroidectomy. G I: 179 patients operated in 1995-2002. In this period we performed systematic FS. Sensitivity (S), specificity (E) and predictive values (PPV, NPV) are analyzed. G II: 126 patients were operated between 2003-2008. Selective FS was performed (23 patients). Both groups are compared: hospital stay, number of FS, percentage of cancer, definitive biopsy and reoperations.', 'Data analyzed in the first period: S: 48%, E: 100%, PPV: 100%, NPV: 90%, positive likelihood ratio>10, negative likelihood ratio 0.52. When both periods are compared no significant differences between reoperations are found.'] Does [ Frozen section do n't reduce the number of reoperations for cancer after hemithyroidectomy ]?