The goal of this work was to evaluate retrospectively, as quality control, the accuracy of frozen section diagnosis in ovarian tumors. We compared 243 frozen section results with the final diagnosis in paraffin sections, from cases studied from January 1994 to April 1999. Results with the two methods were analyzed on two parameters: (a) malignant potential and (b) histological type. As for malignant potential, frozen section diagnosis agreed with the paraffin diagnosis in 94% of all cases (98.5% for malignant tumors, 94% for benign tumors, and 78.6% for borderline tumors). There was one false-positive and 13 false-negative cases. Sensitivity and specificity values for malignant tumors were 93 and 99%; for borderline tumors, 61 and 99%; and for benign tumors, 98 and 93%. With respect to histological type, in 203 cases (84%) the pathologists had no doubt in the diagnosis; in 40 cases (16%) diagnosis was given as compatible with. In 35 of these (87.5%) the initial diagnosis was confirmed by paraffin. Frozen section diagnosis seems to be a reliable method for ovarian tumors, with high sensitivity for malignant neoplasms and a low false-positive rate which allow the best choice of treatment. The most frequent problems arise with borderline and granulosa cell tumors.81230-2