Retinoblastoma usually manifests before five years of age. Retinoblastoma in an adult is extremely rare. Twenty-three cases of retinoblastoma in adults 20 years or older have been reported in world literature. We report a case of adult onset retinoblastoma in a 29-year-old female. Our patient had unilateral endophytic retinoblastoma with vitreous seeds and calcification on ultrasonography. She underwent enucleation with silicone ball implantation and the diagnosis was confirmed histopathologically. The diagnosis of retinoblastoma should be kept in mind in cases presenting with a white mass lesion of unknown etiology, in the fundus of an adult.