Approximately 20% to 40% of the patients with a FIGO I ovarian tumor die within five years after the diagnosis. Morphologic studies (typing and grading) of the primary tumor are prognostically important, but poorly reproducible. Therefore, the prognostic value of more objective techniques, such as morphometry and flow cytometric (FCM) DNA determinations, were evaluated in 33 adequately staged FIGO I patients with at least a five-year follow-up. The overall five-year survival in the group was 64%. Three patient categories were defined on the basis of two easily measured morphometric features, the mitotic activity index (MAI) and the volume percentage epithelium (VPE), which an earlier study had proved to be significantly associated with prognosis. The five-year survival rates were 91% for 11 patients in category A (MAI less than 30 and VPE less than 65), 67% for 9 patients in category B (MAI less than 30 and VPE greater than or equal to 65) and 38% for 13 patients in category C (MAI greater than or equal to 30). FCM showed 25 of the tumors to be diploid and 8 to be aneuploid. The cellular DNA content was also of prognostic value: the five-year survival figures for patients with diploid and aneuploid tumors were 68% and 37%, respectively. Combination of the morphometric and FCM features showed that, in diploid tumors, the morphometric features have additional prognostic value: the diploid-tumor-patient survival rates in categories A, B and C were 91%, 63% and 50%, respectively. None of the eight patients with aneuploid tumors fell in the morphometrically favorable category A while seven were in category C.(ABSTRACT TRUNCATED AT 250 WORDS)