Contrast extravasation on computed tomography angiography (CTA) is rare but becoming more common, with increasing use of CTA for various cerebral vascular diseases. We report on two cases of spontaneous subarachnoid hemorrhage (SAH) in which the CTA showed a saccular lesion of the upper basilar trunk suggesting a ruptured aneurysm. However, no vascular lesion was observed on immediate subsequent digital subtraction angiography (DSA). In one case, repeated follow up DSA was also negative. The patient was treated conservatively and discharged with no neurologic deficit. In the other case, the patient showed sudden mental deterioration on the third hospital day and her brain CT showed rebleeding. The immediate follow up DSA showed contrast stagnation in the vicinity of the upper basilar artery, suggestive of pseudoaneurysm. Double stent deployment at the disease segment was performed. Due to the frequent use of CTA, contrast extravasation is an increasingly common observation. Physicians should be aware that basilar artery extravasation can mimic the appearance of an aneurysm.