The first case of an intracranial plasma cell granuloma is presented. An associated polyclonal gammopathy was another remarkable feature. Routine and special stains of histologic sections as well as electron microscopy characterized such lesions. Immunofluorescent studies revealed a heterogeneous population of plasma cells. When the granuloma was removed, the polyclonal gammopathy resolved, and neither have recurred with eight months of follow-up. It is suggested that prior reports of meningiomas with conspicuous plasma cell-lymphocytic components may in reality be plasma cell granulomas and could be differentiated by electron microscopy.