Intraoperative consultation is a high-risk procedure of pathology departments with important consequences. Therefore, it is critical to determine institutional efficiency of frozen section performance periodically. Frozen section diagnoses of 552 specimens from 401 cases between June 2001 and January 2005 were rewieved and correlated with subsequent histopathological examination, to assess concordant, discordant and deferred diagnoses as well as false negative and false positive rates and to determine reasons for discordance. Each individual specimen from the same case was considered and evaluated as one case. Excluding deferred diagnosis constituting 4.53% of the cases, accuracy, false negative and false positive rates were consecutively found 97.47%, 2.08%, and 0.57%. Interestingly, a great proportion of false negative cases were found to be associated with papillary carcinoma of thyroid. Gross sampling error and misinterpretation appeared as the leading reasons for frozen section discordance. Considering discordant frozen section diagnoses have a great impact on patient’s care, intra and interinstitutional monitoring of frozen section performance may serve as a quality control programme.[Turk J Cancer 2006;36(4):157-161].