The pineal gland and retina share histogenetic features that reflect a similar neurosensory/photosensory ontogeny. Pineal parenchymal tumors demonstrate a highly variable and incomplete photosensory differentiation evidenced by specific cytoarchitectural features and the expression of photosensory retinal S-Antigen (S-Ag). Despite these neuro-ontogenetic parallels, pineal parenchymal tumors have not been well studied for the neuroretinal phenotypes that accompany normal neuroretinal development. The investigation of photoreceptor gene expression may provide an important insight into the histogenesis of pineal parenchymal neoplasms. In this study, a pineal parenchymal tumor of the "mixed pineoblastoma/pineocytoma" type was examined for the expression of several photoreceptor, glial and neuronal proteins including: interphotoreceptor retinoid-binding protein (IRBP), rod opsin, cone opsin, S-Ag and cellular retinaldehyde-binding protein (CRA1BP). The detection of IRBP and its mRNA, the earliest photoreceptor-associated protein expressed during retinal development, corroborated the rudimentary photosensory differentiation of this tumor which had limited cytoarchitectural evidence for pineal differentiation. The analysis of IRBP expression may facilitate the diagnostic recognition of primitive pineal neoplasms and further define the neuroretinal differentiation which occurs in pineal parenchymal tumors.