Paraffin blocks from 17 granulosa tumors, nonmetastatic (n = 10) and metastatic (n = 7), were analyzed by flow cytometry. Three neoplasms, one with and two without metastases, were found to have cells with an abnormal DNA (DNA aneuploid) content. The occurrence or absence of DNA aneuploid cells did not predict behavior. In addition, there was no correlation of tumor DNA content with tumor size or patient age at the time of surgery. There was no significant difference in cell proliferation (%S + %G2/M) between metastatic and nonmetastatic DNA diploid tumors, however, there was an increase in cell proliferation in tumors with a DNA aneuploid stemline. Granulosa tumors are low-grade neoplasms. At least 90% are seen in Stage 1, and metastasis occurs subsequently in 5% to 15% of these cases. Features of Stage I neoplasms associated with subsequent metastasis in some reports, but not all, are involvement of the capsule (Stage IC), large size, and high mitotic rate.'-' Providing definitive statements about the behavior of granulosa tumors is hampered by their rarity, the subjectivity of the diagnosis, and their sluggish behavior. We attempted to determine if flow cytometric analysis of DNA could identify granulosa tumors with metastatic potential. We compared DNA histograms from ten Stage 1A granulosa tumors that did not metastasize during 22 to 47 years of follow-up with seven granulosa tumors that showed malignant behavior.