We reviewed 4057 intraoperative frozen sections from 1980 through 1984 to assess the accuracy, strengths, and weaknesses of this technique. Breast, lymph node, and skin comprised half of the sites evaluated. Frozen-section and final diagnoses agreed in 91.5% and disagreed in 6.8% of the cases; 1.7% of the cases were deferred. False-negative frozen-section diagnoses were due to pathologist sampling or judgment errors and surgeon sampling errors. There were eight (0.15%) false-positive diagnoses, none of which altered patient treatment. We recommend that lymph nodes for lymphoproliferative disorders and breast tissue for which a malignant diagnosis will not result in an immediate mastectomy not be submitted for frozen-section diagnosis. Appropriate studies of these tissues can be carried out without an intraoperative diagnosis; such a policy will increase the cost-effectiveness of frozen sections without compromising patient care.