Expression of proliferating cell nuclear antigen, a DNA polymerase delta auxiliary protein, was studied in 20 specimens from 20 patients with conjunctival malignant melanoma by means of the total number of cells that showed immunoreactivity per square millimeter. The countings were shown to be reproducible with minimal intraobserver variability. In a multifactor analysis of variance (ANOVA) that adjusted for possible confounders, patients who subsequently died of metastatic disease had significantly higher counts of cells that were positive for proliferating cell nuclear antigen per square millimeter (P = .0011) than patients with a minimum survival of five years without clinical signs of metastatic disease. A multivariate Cox regression model confirmed the independent prognostic value (P = .048) of the cell counts. Individual hazard ratios were estimated in a final Cox model and two groups of patients with low and high hazard ratios were formed. Five-year cumulated survival proportions of the two groups were 90% and 60%, respectively. The total count of cells displaying immunoreactivity for proliferating cell nuclear antigen per square millimeter may be used as a prognostic indicator in patients with conjunctival melanoma.