Introduction: Mycotic aneurysms are a rare pathology, but not negligible, having to think about it in all patients with suspected infectious process, because it is an entity in which if delayed diagnosis worsens the prognosis, increasing complications and mortality.

Case report: 80-year-old, pluripathological man, came to our hospital because of weakness in both lower limbs, fecal and anal incontinence, and right L1 territory anesthesia. Dural fistula diagnosed at T12-L1 level and is successfully resolved surgically. During admission it has recurrent urinary tract infections. Three days after surgery presented right central facial paralysis. Cranial CT is performed, which shows a subdural hematoma without surgical criteria. Three hours later the patient presented deterioration of neurological status (GCS 4) and bilateral non reactive mydriasis. He had a urgent surgery in where is observed a large acute subdural hematoma and fusiform aneurysm in right M4. It was excluded from the circulation. The patient died three days later.

Discussion: Cerebral aneurysms of an infectious origin often have a disastrous clinical course in which morbidity and mortality can be reduced by early diagnosis, appropriate antimicrobial therapy, and aneurysm elimination.