A sixty-two-year-old woman was diagnosed as having the mitral valve insufficiency seven months prior to admission. The patient was admitted to the hospital with complaints of right hemiparesis and aphasia. CT scan revealed an intracerebral hematoma in the left front-parietal region. Cerebral angiography disclosed an aneurysm at the distal portion of left middle cerebral artery. An increase in the amount of C reactive protein and leukocytosis indicated the presence of inflammatory lesions. Antibiotics were administered because a mycotic aneurysm was suspected. White blood cell count and C reactive protein returned to normal after treatment with antibiotics for one months. The aneurysm had disappeared on the second angiography performed after treatment. Strategy for mycotic aneurysm is still controversial. 49 reported cases in the literature since 1975 were reviewed and the efficiency of antibiotic therapy was discussed.