Seizures are common neurological emergencies that occasionally cause prolonged impairment of consciousness. The aim of this retrospective single-center study is to clarify factors associated with prolonged impairment of consciousness for admitted adult patients investigating patient backgrounds, blood tests, electroencephalographic patterns, and MRI findings. The patients who were admitted to the hospital due to epileptic seizures were classified into two groups: (1) early recovery group, in which patients recovered their consciousness within 6 hr, and (2) delayed recovery group, in which patients showed impairment of consciousness more than 6 hr. Factors associated with prolonged impairment of consciousness were compared between these groups. In this study, 42 cases (33 patients), with a mean age of 67.8 years, were included. Fifteen cases (13 patients) and 27 cases (20 patients) were classified into the early and delayed recovery groups, respectively. The populations of older patients and patients from a nursing home were significantly higher in the delayed recovery group. With regard to radiological analyses, a high grade of periventricular hyperintensity (PVH), high Evans index score, and enlarged bilateral atrial widths were significantly associated with prolonged impairment of consciousness. Multivariable analyses showed that a high grade of PVH was significantly associated with delayed recovery of consciousness independent of age and status epilepticus. In conclusion, we proposed that diffuse white matter degeneration around the lateral ventricles contributes to prolonged impairment of consciousness.