The neuroradiologic observations on a case of growing giant intracranial aneurysm originating from a small saccular aneurysm are described in detail. The reports in the literature of growing giant aneurysms are reviewed. The computed tomographic and angiographic findings are described and special diagnostic difficulties analyzed. A correlation between the computed tomographic and neuropathologic findings is made, and the pathogenetic mechanisms of enlargement of aneurysms are discussed.