A 13-year-old boy, whose bilateral retinoblastoma had been treated by enucleation (OD) and irradiation (OS), developed anterior staphyloma (OS) necessitating the second enucleation. Histopathological, immunohistochemical and electron microscopic studies revealed malignant teratoid medulloepithelioma of the ciliary body, with demonstrated multipotential histogenesis. This is the first report which demonstrates the development of a second malignant intraocular tumor in an eye previously affected by hereditary retinoblastoma. Careful monitoring of patients who have had hereditary retinoblastoma is necessary because of the potential for a second malignancy.