Late-onset epilepsy has been linked with accelerated cognitive decline and a higher risk of dementia. In this study, we sought to characterize the cognitive profile of participants with late-onset unexplained epilepsy and compare their MRI findings to healthy controls, to better understand underlying disease mechanisms. We recruited participants with at least one new-onset unexplained seizure at age 55 or later, without cortical lesions on MRI, within 5 years of the first seizure. We administered a neuropsychological battery to generate Preclinical Alzheimer Cognitive Composite and composite scores for delayed verbal recall, processing speed and executive function. We held a consensus meeting to determine whether the participants fulfilled criteria for mild cognitive impairment. An MRI volumetric analysis of hippocampal, amygdalae, and white matter hyperintensity volume was performed and compared to 353 healthy controls from the Harvard Aging Brain Study. On late-onset unexplained epilepsy participants, we also obtained 24-h EEG recording. Seventy participants were recruited, mean age 71.0 ± 7.0 years, 49% female, 15.6 ± 3.0 years of education. Impaired cognition (