A clinicopathologic and follow-up study of 56 intraocular medulloepitheliomas in the Registry of Ophthalmic Pathology revealed a mean age of five years at the time of definitive diagnosis, most patients having had a delay in surgical therapy of more than one year after onset of signs or symptoms. Histologic evidence of malignancy was observed in 37 tumors, and follow-up studies revealed four patients to have died of metastatic disease. Heteroplastic elements (brain tissue, cartilage, or rhabdomyoblasts) were observed in four benign and 17 malignant tumors; these 21 were designated teratoid medulloepitheliomas. The most important prognostic feature was extraocular extension, observed in ten cases. All four of the known tumor deaths were preceded by clinically obvious orbital spread. In four additional cases with orbital involvement the patients were lost to follow-up. We concluded, therefore, that the prognosis is worse than the results of this study would indicate, especially among those cases observed to habe extraocular extension.