Acute isolated sphenoid sinusitis is a relatively uncommon entity. Because its symptoms and clinical findings are nonspecific, it can be easily misdiagnosed. Left unrecognized and untreated, it can lead to several well-known and severe complications, including meningitis, cerebral abscess, cavernous sinus thrombosis, and epidural or subdural empyema. We report the case of a 28-year-old woman with acute sphenoid sinusitis complicated by ischemic stroke in the left caudate nucleus, lentiform nucleus, and posterior part of the internal capsule. The stroke was diagnosed on magnetic resonance imaging. Also, magnetic resonance angiography showed a narrowing of the internal carotid artery and a narrowing of the first part of the left anterior and middle cerebral arteries (A1 and M1 segments). The patient was treated with medical therapy, including antibiotics, and surgical drainage of the sphenoid sinus via an endoscopic approach. Her outcome was good, and she experienced minimal neurologic sequelae. We discuss the possible explanations for this rare complication.