Cerebral air embolism caused by lung cancer is extremely rare, especially if not associated with invasive procedures such as needle biopsy. We describe the case of an 86-year-old man with squamous cell lung carcinoma of the left lung. He developed a bad cough and subsequently suffered left hemiplegia. Brain computed tomography (CT) on admission showed no abnormal findings. Diffusion-weighted magnetic resonance (MR) imaging revealed high intensity lesions in the right frontal lobe and right parietal lobes. Repeated brain CT revealed air densities around the high intensity lesions on previous MR imaging, compatible with air embolism causing cerebral infarction. Chest CT confirmed a left pulmonary hilar mass invading the left pulmonary vein, left atrium, and main bronchus. Air densities were found in the left heart ventricle. These radiological findings were attributed to cerebral air embolism associated with advanced lung cancer. Shortly afterwards he died of progressive respiratory failure. Our case reveals two important aspects. First, cerebral air embolism can be caused by lung cancer invading the pulmonary vein, left atrium, and main bronchus without iatrogenic causes. Therefore, we should pay special attention to the etiology when the patients with lung cancer in the advanced stage developed cerebral infarction. Second, repeated CT is recommended if cerebral air embolism is suspected because initial head CT does not always reveal air bubbles.