An 86-year-old woman with a history of hypertension, hyperlipidemia, coronary artery disease, and hypothyroidism sought care for subacute, progressive cognitive decline. Five months earlier, she was hospitalized for a small, left temporal, lobar, intracerebral hemorrhage with associated receptive aphasia. Over the next several months, she had a precipitous cognitive decline. She was prescribed memantine by her primary physician because of concern for dementia. One month before seeking care, she was found unconscious in her bathroom, which was believed to be an unwitnessed seizure. Brain magnetic resonance imaging 1 month before the current evaluation showed a prior, small, left temporal hemorrhage and diffuse lobar microhemorrhages on gradient echo imaging, focal leptomeningeal gadolinium enhancement in the left temporal lobe, and multifocal T2 hyperintensity with mass effect, maximal in the left temporal lobe. Electroencephalography showed multifocal, independent epileptiform discharges. She underwent open biopsy of the left temporal lobe, which indicated focal granulomatous inflammation causing vascular destruction, with β-amyloid plaques within the cortical and leptomeningeal vessels. The findings were consistent with a diagnosis of amyloid-β-related angiitis in the setting of severe cerebral amyloid angiopathy. Because of concern for subclinical seizures and epileptiform discharges on electroencephalography, the patient was started on levetiracetam without substantial change in her mental status. After the biopsy findings demonstrated inflammatory changes consistent with amyloid-β-related angiitis, she was started on intravenous methylprednisolone, followed by transition to prednisone. After 6 months of treatment, she had significant clinical and radiographic improvement. Follow-up magnetic resonance imaging at that time showed interval improvement in the T2 hyperintensity and mass effect in the left temporal lobe. She was again independent with her activities of daily living, and memantine was discontinued. Cerebral amyloid angiopathy encompasses a heterogeneous group of diseases characterized by amyloid-β peptide deposition. The most common clinical manifestation of cerebral amyloid angiopathy is lobar intracerebral hemorrhage, which can be multifocal and recurrent but can also result in cerebral ischemia and ischemic leukoencephalopathy.