A 38-year-old woman was admitted to our hospital with a 3-day history of severe headache associated with some nausea and vomiting. MRI did not show any evidence of subarachnoid hemorrhage, but MRA and CTA showed an aneurysm on the paraclinoid region of the right internal carotid artery. She was successfully treated by coil embolization. MRA taken 7 days after the treatment showed marked vasospam. Fortunately, her therapeutic course was uneventful and she was discharged without any neurological deficits. Vasospasm without subarachnoid hemorrhage is a rare event. Here, we review the literature and discuss potential mechanisms for vasospasm in the absence of subarachnoid hemorrhage.