Retinoblastoma is the most common childhood intraocular tumor, occurring in 1 of 18,000 live births. Retinoblastoma may occur as a germinal mutation or a somatic mutation. Forty percent of retinoblastoma cases are caused by a germline mutation and include those patients with a positive family history of the disease. Children with hereditary forms usually have multifocal, bilateral retinoblastoma, whereas children with the somatic form have unilateral, unifocal disease. However, up to 15% of cases of sporadic unilateral retinoblastoma may be hereditary. It is important to recognize that this subgroup of unilateral patients remains at risk for the development of second tumors as well as second primary tumors of the intracranial midline, or "trilateral retinoblastoma." We report a case of a 2-month-old child with unilateral retinoblastoma in whom pinealoblastoma subsequently developed.