We studied the mechanism underlying seizure induction in patients with chronic subdural hematoma. In our study population of 1,009 patients with chronic subdural hematoma, 26 (2.6%) had seizure-related complications. Six of them had already been diagnosed with epilepsy (4 patients) or suspected of having secondary epilepsy (2 patients) after experiencing traffic accidents or cerebral bleeding. Twenty patients (seizure group) had been tentatively diagnosed as having hematoma-induced convulsion. Of the remaining 989 patients without convulsion, 40 randomly sampled patients were included in the non-seizure group by matching with clinical terms. Intergroup comparisons showed that patients with dementia were more common in the seizure group than in the non-seizure group; however, no intergroup differences were observed for other clinical parameters. Radiological examinations showed that bilateral hematomas were relatively more common and sulcal hyperintensity on FLAIR MR images was significantly more frequent in the seizure group than in the non-seizure group. Interestingly, many patients presenting with sulcal hyperintensity exhibited mixed-density hematomas on CT images. These findings suggest the mechanism by which hematoma content infiltrates into the brain parenchyma and the subsequent induction of convulsions by the stimulatory component.