Chikungunya, a viral infection that presents with fever, rash and polyarthritis, is usually an acute febrile illness. Uncommon neurological manifestations include meningoencephalitis, encephalitis, myelitis, Guillain-Barre syndrome, myelopathy and neuropathy. During an outbreak of the disease in La Reunion Island, abnormalities were observed in the magnetic resonance imaging (MRI) of patients with encephalitis and acute disseminated encephalomyelitis, showing bilateral, frontoparietal, white matter lesions with restricted diffusion, similar to our case. We report a 57-year-old male patient with comorbidities, admitted with high fever, arthralgia, asthenia, vomiting, psychomotor agitation, behavioral changes and seizures. Cerebrospinal fluid (CSF) values revealed pleocytosis (98 cells/mm3 with 68% lymphocytes and 12% monocytes) and high levels of protein (161 mg%). Brain MRI showed hyperintense lesions in the temporal and frontal lobes and bilaterally in the posterior thalamus. CSF serology was positive for IgM antibodies to Chikungunya virus. Encephalitis due to an acute viral infection by Chikungunya was diagnosed. The patient's clinical condition worsened and he died on the twenty-fourth day of admission to our hospital.