A 22-yr-old red-tailed boa constrictor (Boa constrictor constrictor) was evaluated for neurologic abnormalities, including cervical weakness and right-sided optical and thermal blindness. Previous diagnostic testing of this individual had ruled out inclusion body disease of boids as a cause of the neurologic signs. Magnetic resonance imaging (MRI) with the use of both a 7-T research unit and a 1.5-T clinical unit was performed, and confirmed the diagnosis of a large mass within the diencephalon and mesencephalon causing hydrocephalus and asymmetry of the lateral ventricles. Both MRI units provided diagnostic images. Based upon the lack of surgical or medical options for treatment, euthanasia was elected. Necropsy and histopathology confirmed the presence of an intracranial mass, with gross images closely mirroring those noted antemortem with MRI. The mass was likely to have an ependymal or astrocytic origin based on immunoreactivity of neoplastic cells to glial fibrillary acidic protein and caused complete compression and/or effacement of components of the diencephalon, including the thalamus and pineal gland, as well as the mesencephalon. This case illustrates the neurologic deficits, application of advanced MRI for neuroimaging, and immunohistological characteristics of an uncommon primary neural neoplasia in a snake.