A 50-year-old man presented with an aneurysm arising from a fenestration of horizontal portion (A(1)) of the anterior cerebral artery manifesting as subarachnoid hemorrhage. Coil embolization was conducted and the aneurysm was occluded easily. Most reported cases of these types of aneurysms underwent direct surgery. Aneurysm arising from the A(1) fenestration is rare, but the present case shows that coil embolization can be an effective treatment modality. Three-dimensional rotational angiography and aneurysmography were helpful to characterize this complicated vascular structure.