A 40-year-old man presented with a left optic neuropathy. Magnetic resonance imaging demonstrated a contrast-enhancing mass along the course of the left trigeminal nerve and in the region of the left cavernous sinus with suprasellar extension. Preoperatively, he had a serum polyclonal gammopathy. Pathologic diagnosis was an intracranial plasma cell granuloma. The patient responded to high-dose steroids with resolution of his optic neuropathy, marked decrease in the size of the mass, and resolution of the serum polyclonal gammopathy. Intracranial plasma cell granuloma is a rare lesion; only 11 cases have been described in the literature. Almost half of the patients presented with vision loss as their chief complaint.