Rasmussen syndrome (RS) is a rare encephalitis characterized by inflammation of one cerebral hemisphere that causes atrophy, neurological and cognitive impairment. We present a 42-year-old female patient, with no significant previous history and diagnosed with epilepsy since she was 24 years old, epileptic seizures are reported in different time windows with temporary cessation, but with constant reinstallations of acute and drug-resistant episodes. Neurological examination revealed hyperkinesia of the extremities, with persistent flexion and extension movements. The neuropsychological evaluation carried out with the MoCA test, Rey’s complex figure and Token test, shows severe cognitive impairment with psychiatric symptoms. In addition, electroencephalogram results show unilateral hemispheric slowing with unilateral focal onset and MRI evidence of generalized atrophy of the left hemisphere, elements supporting the diagnosis of late-onset RS. Finally, information is offered about the associated neuropsychological manifestations.