Nonconvulsive status epilepticus (NCSE) is a severe medical condition that shows increased incidence in the elderly and is frequently underdiagnosed because of its pleomorphic presentation. We report an NCSE in a 76-year-old woman affected by dementia with acute change of cognitive status and behavior. Intravenous diazepam solved clinical and electroencephalographic manifestations. Neuropsychological assessment after NCSE conclusion showed impairment of several fields that remained unchanged at 3-month followup. NCSE should be considered when sudden and transient cognitive fluctuations appear in the elderly. Epileptic events in dementia occur frequently and are often underrecognized; this could be a misleading factor when considering a quick progression of mnesic performances. Moreover, recent findings both in animal models and in humans demonstrated the deep link between epilepsy and dementia, also supporting the hypothesis that epileptiform activity could contribute to cognitive impairment.