Despite the widespread use of the pipeline embolization device (PED), no complete aneurysm regrowth after its placement has been reported in the literature. We report the first case of aneurysm regrowth after the initial follow-up angiography demonstrating near-complete occlusion of the aneurysm and remodeling of the vessel with on-label PED use for a large 20 mm × 24 mm × 22 mm (width × depth × height) cavernous segment internal carotid artery (ICA) aneurysm. The patient was treated with two overlapping PED (4.5 mm × 20 mm and 5 mm × 20 mm). Follow-up angiogram at 4 months after treatment demonstrated remodeling of the ICA with a small residual component measuring approximately 7 mm × 8 mm × 7 mm. However, at 10 months after treatment, there was a complete regrowth of the aneurysm with interval growth, now measuring 25 mm × 28 mm × 18 mm. Despite the high aneurysm occlusion rates reported with the PED, persistent aneurysm filling and aneurysm regrowth, although rare, should not be overlooked.