Retinoblastoma is the most common childhood primary intraocular malignancy, with the majority of cases being diagnosed before 5 years of age. Retinoblastoma in adults is extremely rare. Here, we report the case of a 20-year-old man who presented with a 3 year history of blurred vision in the right eye. Imaging did not reveal the typical presentation of retinoblastoma. After considering Coats' disease, a diagnosis of late-presenting retinoblastoma was made through cytological analysis. Diagnosis of retinoblastoma should be considered in the presence of uncertain mass lesions in the fundus of an adult.