An unusual lymphoid lesion with reactive germinal centers, occurring in the choroid plexus of a young gorilla, is reported. It presented as a large mass in the lateral ventricle with hydrocephalus and neurological symptoms. A work-up did not reveal any underlying cause for this lesion. No similar lesion of the choroid plexus has been reported in either human or veterinary literature. Histological work-up, including flow cytometry, gene rearrangement studies and T and B cell markers, favored the lesion being a non-neoplastic lymphoid proliferation of unknown etiology. The prognosis is unknown, although, following complete removal, the animal is well and free of tumor at the time of this report.