Rasmussen's encephalitis (RE) is a chronic, progressive disease that typically occurs in childhood, rarely in adulthood. When it does occur in adulthood, it may be associated with atypical electro-clinical features, and neuroimaging alterations usually help diagnosis. Unlike childhood forms, in which epilepsia partialis continua is usually observed, the EEG pattern in adult variants may be aspecific. We describe a highly interesting case of late-onset RE in which an electrical status epilepticus was not detected by the surface EEG, but by a recording with subdural electrodes.