Few reports exist on the pathologies of the northern bottlenose whale (Hyperoodon ampullatus) and other Ziphiidae. We here describe a large exostosis in the right pterygoid bone of adult female H. ampullatus ANSP-3004 that stranded on the US Atlantic coast in 1867. Images of the skull and 14 cranial measurements were examined and compared with two ‘normal’ adult female H. ampullatus specimens. Surface scans of ANSP-3004 were made with a Faro Design Arm 1.0 scanner at 75µm resolution. The form, structure and width (15.9 cm) of the right pterygoid were found to be abnormal. Its distal extremity was curved in labial direction while its proximal extremity was deformed by a large, bulbous exostosis of 14.3 x 12.5 cm that partially obstructed the right nasal passage. Lytic lesions in the posterior end of the exostosis exposed deep resorption lacunae. The left pterygoid was thin (3.4 cm) and laterally displaced. No diagnosis was possible for lack of histological examination but the osteopathy was consistent with osteoma, a benign bone tumor commonly seen on the jaws and nasal sinuses of bovines, phylogenetical relatives of Cetacea. The partial nasal passage obstruction may have affected respiration to some degree, but since the female was lactating, general fitness appeared stable.