A neoplastic cerebral aneurysm from lung cancer is an extremely rare occurrence despite its high metastatic potential to the brain. We report a neoplastic cerebral aneurysm from small-cell lung carcinoma that caused an intracerebral hematoma. A 63-year-old man underwent an urgent craniotomy for a massive intracerebral hematoma. After evacuation of the hematoma, an anomalous artery was found on the wall and a biopsy was done. The histological examination revealed that the artery was filled with neoplastic cells, and a part of the vessel wall was distended, forming an aneurysm. The histological feature of the tumor cells was consistent with small-cell lung carcinoma, which was disclosed in the left hilus.