Recent advances in flow cytometry allow for study of DNA content in paraffin-embedded pathology material. Using refinements of published techniques, we retrospectively correlated tumor cell DNA content (ploidy) with histologic findings and clinical outcome in 79 patients with uveal melanoma. Patients were included using these selection criteria: enucleation without adjunctive therapy performed at the University of California at San Francisco between 1956 and 1979, tumor located in ciliary body or choroid, and pathology material and complete follow-up data available. The DNA histograms were classifiable as diploid or hyperploid in 64 cases. The mean coefficient of variation for diploid histograms was 6.6%. Twenty-three patients (36%) had hyperploid tumors. Hyperploidy was correlated with worse outcome. The effect was most marked for DNA indexes of over 1.4. A Cox proportional hazards model showed that the effects of tumor diameter and cell type were insignificant in comparison with the effect of the DNA index.