Aneurysm affecting the distal segment of anterior cerebral artery (DACA) are well documented. But scanty literature is available on the structural and morphological changes produced by the aneurysm on the brain tissue which in turn can produce clinical effects and functional disturbances. Distal cerebral artery aneurysms represent 1.5% to 9% of intracranial aneurysms and most often occur at the origin of the calloso-marginal artery. Frontal lobe plays a vital role in higher mental functions such as motivation, planning, social behaviour and speech production. Damage to frontal lobe can show cognitive, emotional, behavioural symptoms. We present a case report of a completely thrombosed unruptured intracranial aneurysm (UIAs) of anterior cerebral artery proximal to origin of calloso-marginal artery in a cadaveric brain. This space occupying lesion in this particular case may be considered as one of cause for progressive frontal lobe syndrome. Therefore, it is desirable to identify UIA’s which are at greater risk of rupture and those which may cause slow progressive space occupying lesion, while considering which to repair.