This report describes a 69-year-old woman who presented with acute monocular visual loss, ipsilateral headache, and elevated sedimentation rate (ESR) and C-reactive protein (CRP). Both temporal artery biopsies were negative. Neuroimaging, dural biopsy, and breast biopsy all confirmed the diagnosis of carcinomatous hypertrophic pachymeningitis associated with metastatic breast carcinoma. After treatment with corticosteroids, her vision improved. Her clinical presentation initially mimicked the symptoms and signs of giant cell arteritis. Acute monocular visual loss without other cranial nerve palsies may be an uncommon presentation of hypertrophic pachymeningitis from metastatic breast carcinoma.