A 28-year old man presented with decreased vision and a bitemporal hemianopia. Magnetic resonance (MR) imaging demonstrated what appeared to be an enlarged optic chiasm and, on T2-weighted images, hypersignal extending along the optic tracts. This was felt to represent an intrinsic chiasmal mass, most likely a chiasmal glioma. Biopsy specimens from the first craniotomy were nondiagnostic. With continued visual failure, the patient underwent a second operation, and the correct diagnosis of craniopharyngioma was established. This article emphasizes the difficulties encountered with neuroradiology evaluation and histopathologic study of craniopharyngioma. © 1992 Raven Press, Ltd., New York.