High-resolution computerized tomography of the orbit was performed in patients with histologically proven retinoblastoma to assess the efficacy of CT in delineating the retro-orbital extent of the tumor and determining if the optical nerve was involved. High-resolution CT proved able to accurately delineate tumor size, tumor localization, tumor calcification, retro-orbital and intracranial tumor growth. Microscopical tumor spread past the lamina cribrosa of the optic nerve, however, could not be detected by CT.