By selectively infiltrating and destroying the internal elastica of a major cerebral artery, Aspergillus fungus (Af) induces disruption and incipient dilatation of the vascular wall with or without inflammation. This unique pathogenetic mechanism of forming "true" fungal mycotic aneurysms (FMAs) was clearly demonstrated in a middle-aged adult male who died of a pontine stroke. The latter was secondary to thrombosis in the basilar artery of which the internal elastica was infiltrated and replaced by Af hyphae. The patient had diabetes, liver cirrhosis with oesophageal varices, and received multiple blood transfusions. However, leukopenia was not present and immunosuppressive drugs were not used. This case prompted comparison of the natural history and pathogenesis of bacterial and fungal mycotic aneurysms in cerebral arterial branches. Selective destruction of the internal elastica with progressive dilation at a segment of vascular wall insinuates a potential pathogenetic process involved in the formation of saccular or berry aneurysm. Management and therapeutic approaches for FMA are discussed.