Some anatomical variations in the A1 segment of the anterior cerebral artery have been reported, but large cortical branches arising from this A1 segment are rare. Herein, we report an unusual case of a callosomarginal artery originating from the A1 segment associated with an unruptured aneurysm and distal A1 fenestration in an 85-year-old woman. These variants and aneurysm were incidentally identified on magnetic resonance angiography performed for the evaluation of cerebral infarction. Magnetic resonance imaging is useful in identifying anomalies in cerebrovascular structures. Conservative management was selected because of the small size of the aneurysm and the patient's advanced age.