The nuclear DNA content and S-phase fraction of 23 ovarian granulosa cell tumors were measured from paraffin-embedded tissue with flow cytometry. Crude survival of the patients with a euploid tumor (17 diploid, one tetraploid) was more favorable than that of the patients with an aneuploid tumor (n = 5, P = 0.02). The percentage of S-phase cells was a good predictor of survival. If more than 6% S-phase cells were present in the DNA histogram, both crude survival (P = 0.0001) and survival corrected for intercurrent deaths (P = 0.0001) were clearly inferior as compared with tumors with less than 6% S-phase cells. The results indicate that DNA flow cytometric study may provide a rapid and valuable method to predict the biological behavior of granulosa cell tumors of the ovary.