Giant cell arteritis (GCA) is a disease chiefly found in elderly patients. Intracranial vessels are rarely involved in GCA. Here we report the case of a 19-year-old woman with GCA in the basilar and vertebral arteries. Two weeks after the first symptoms, she developed an aneurysmatical dilatation of the right vertebral artery which ruptured leading to subarachnoid hemorrhage. Although the ruptured right vertebral artery was clipped neurosurgically, she died two days later. Autopsy revealed GCA with focal medial necrosis and intimal thickening of the vertebral arteries and the basilar artery. No other arteries were affected. In the involved vessels, the media exhibited C1q immunoreactivity. At the intimal site of the internal elastic lamina there were increased levels of elastase. Other arterial diseases showing the pattern of GCA were excluded. This case demonstrates that GCA is not necessarily restricted to elderly people. Moreover, this case shows that a GCA-induced aneurysm is a very rare reason for subarachnoid hemorrhage even in young adults.