The study is based upon a review of data from 583 consecutive patients with retinoblastoma over the years 1956 to 1986. Mean follow-up was 8 years, and median was 5.5 years. In 41 patients, metastases developed within 5 years. The influence of clinical and histopathologic risk factors on the occurrence of metastases was first analyzed by univariate tests. Significant variables were then reevaluated using the Cox proportional hazards method. Four factors were found to be independently associated with the development of metastases: optic nerve invasion with and without involvement of the resection line, choroidal invasion and enucleation of an affected eye more than 120 days after initial diagnosis. The 5-year metastatic risks associated with these factors were 67%, 13%, 8%, and 4%, respectively. The relative risk estimate, calculated from the Cox model, was used for a score classification with groups of low, medium, and high metastatic risk. The 5-year incidence of metastases was 4%, 43%, and 68%, respectively.