Three hundred twenty-three eyes enucleated because of intraocular tumor were studied. The microscopic features were compared with survival data from 6 to 21 years after surgery, thus permitting the prognostic value of certain findings to be determined. Of the tumors, 299 were malignant melanomas of the choroid (262 eyes) or the ciliary body (37 eyes). Tumor characteristics taken into consideration were regressive changes, lymphocyte infiltration, size, localization, local spread, and degree of pigmentation. All the parameters studied were percentage-wise wise correlated to each other. Where regressive tumor changes were found the survival prognosis was worse than in the undifferentiated collective as a whole. Tumor growth through the sclera or into blood vessels or nerves was correlated to a higher mortality rate due to metastases. It is remarkable that, of these three types of local proliferation, growth into blood vessels was least prone to cause death due to metastases and that in this group mortality due to metastases during the first year after enucleation was latent. Almost all survival curves were polyphasic with periods of about three years between changes in mortality. Curves showing patient age at enucleation peaked at 50-59 years for those patients still alive today, and at 60-69 years for those who died from metastases. On the basis of the results obtained, a number of hypotheses concerning tumor dynamics and the spread of metastases are discussed.