An 81-year-old female presented with a giant aneurysm of the distal anterior cerebral artery (A3) which grew from a small saccular aneurysm to a huge aneurysm within 36 months before manifesting as a mass lesion. The thrombosed portion of the aneurysm showed growth, whereas the aneurysmal cavity did not change in size. Computed tomography and magnetic resonance imaging showed new bleeding in the thrombosed portion. Hemorrhage into the thrombus and/or aneurysmal wall might have caused the aneurysmal growth. She refused surgery and was discharged with no deficits. Distal anterior cerebral artery aneurysm which shows neuroimaging signs of growth requires regular follow up as such lesions may become giant before manifesting clinical symptoms.