Retinoblastoma in an adult is extremely rare. This tumor is most common before the age of two and rarely occur after the age of seven. In 1929, Verhoeff reported a well-documented retinoblastoma in a 48-year-old man. Since that report, about 17 additional cases have appeared in the world literature, but not in the domestic areas. This case report is of a 67-year-old man whose enucleated right eye was found to contain a retinoblastoma. It is believed to be the first recorded instance of retinoblastoma in an adult in Korea. Grossly, the globe was a normal size and shape, measuring 26×25×25㎜. The cut surface revealed two large grayish-white intraocular tumor masses in the temporal and nasal area, measuring 19×12㎜ and 10×4㎜ in its extent, respectively. Microscopically, the tumor consisted of round and oval hyperchromatic cells with scanty cytoplasm. There were typical abundant Flexner-Wintersteiner rosettes, necrosis with multifocal calcification, cholesterol clefts and foreign-body giant cells. The tumor invaded the sclera, but the optic nerve was intact. The pathogenesis of the retinoblastoma occuring in adults seems to be a late development.