When intracranial aneurysms are deemed nonclippable, an accepted alternative neurosurgical treatment is to reinforce the aneurysm wall by wrapping or coating it with various materials, including muslin (cotton gauze). Granulomatous or "foreign-body" reactions, sometimes referred to as "muslinomas" or "gauzomas," and adhesive arachnoiditis are known but rare complications. Experience with MRI in these cases is limited. We describe the clinical and MRI features of a muslinoma developing after treatment of an anterior communicating artery aneurysm.