In this series of 3,432 cases of malignant melanoma of the choroid and ciliary body, mortality from metastasis 15 years after enucleation was 46 per cent. This mortality was at least ten times greater than has been observed with tumors of the iris, probably owing to the greater size and more malignant cytology of choroidal and ciliary body tumors. In 56 per cent of the 3,432 cases, the melanomas were composed of a mixture of spindle and epithelioid cells. The 15-year mortality of patients with melanomas of mixed cell type was three times that of patients with tumors of pure spindle cell type. In 30 per cent of the cases in this series, the melanomas of the choroid and ciliary body were larger than 15 mm in diameter. Size was highly correlated with mortality. The distribution of deaths following enucleation in the 3,432 cases was a log-normal function of time from enucleation. This indicated that metastasis occurred in these fatal cases close to the time of enucleation. The authors were also able to infer that many years were usually required for these uveal melanomas to grow from small (7 to 10 mm in diameter) to large (greater than 15 mm in diameter). These observations are consistent with the hypothesis that dissemination of tumor cells at the time of enucleation has been a major cause of metastasis with small and medium-sized uveal melanomas.