Congenital anomalies of the vertebral artery, including aneurysms and fenestrations, or partial duplication of the extracranial vertebral artery are rarely seen. Presented here is an unusual case of bilateral congenital anomalies of the extracranial vertebral arteries. The right vertebral artery demonstrated an aneurysm and the left a partial duplication. The aneurysm was felt to be the source of the embolic phenomenon to the posterior circulation. This was treated with detachable balloon catheter placement. © 1996 S. Karger AG, Basel.