Cerebral artery fenestration with flow-associated aneurysm is rare among cerebrovascular pathologies. Treatment includes open neurosurgery and/or endovascular treatment. We report a case of a 53-year-old woman with an incidentally detected aneurysm during magnetic resonance tomography. As the underlying cause, a digital subtraction angiography revealed a left internal carotid artery fenestration. Elective endovascular treatment via flow diversion was indicated and a pipeline embolization device was implanted. Follow-up examinations presented a completely occluded additional caudal limb and a decreasing aneurysm size. No clinically adverse events occurred within twenty-four-month post-treatment. Therefore, sole flow diversion was a feasible treatment option in this case.