Isolated cortical subarachnoid hemorrhage is rare and poorly understood. Differential diagnoses and proposed pathophysiology vary widely and the diagnostic work-up for these patients who present with transient ischemic attack-like episodes and characteristic imaging findings is still unclear. We report a case of isolated subarachnoid hemorrhage and transient neurologic deficits due to isolated cortical vein thrombosis that was not detected by noninvasive tests. A 75-year-old woman with a history of a lobar intracerebral hemorrhage presented to the Academic Medical Center with sudden-onset transient left upper extremity weakness. Head CT showed a linear hyperdensity in the right precentral gyrus suggestive of isolated subarachnoid hemorrhage. MRI showed susceptibility in the corresponding area. CT angiogram and MRV showed no evidence of a venous thrombosis. The main outcome measures were results of computerized tomography and CT angiogram, magnetic resonance parenchymal and vascular imaging, angiography findings and clinical follow-up at 3 months. Cortical vein thrombosis was detected on conventional angiography. MRI was negative for microhemorrhages. The patient was anticoagulated and had no recurrences of her symptoms. We conclude that cortical vein thrombosis can present as isolated subarachnoid hemorrhage and transient ischemic attack-like episodes and may require angiography for definitive diagnosis.