A patient with monocular retinoblastoma was examined with the wide-field specular microscope before undergoing enucleation. An unusual image on the corneal endothelium consisted of irregular oval dark structures within which bright reflections formed a lacy network. Light and electron microscopy confirmed these structures to be clusters of retinoblastoma cells adherent to the endothelium. These findings suggest that the specular microscope may aid in the diagnosis of intraocular tumors.