A 57-year-old male agricultural worker with a history of type 2 diabetes and arterial hypertension, presented with high-grade fever, arthralgia, asthenia and vomiting during the eight days prior to admission to our hospital. On the 8th day, he presented with psychomotor agitation, behavioral changes and seizures. A computed tomography (CT) brain scan without contrast was performed and had no abnormalities. CSF analysis presented neutrophilia (72%) pleocytosis (240 cells/mm) with normal glucose and high protein levels. Because of the neurological deterioration, the patient was admitted to our hospital. On admission, hypotension, bradycardia and a reduced level of conscience was observed (Glasgow coma scale 11). On the same day, the patient presented severe dyspnea and was promptly intubated. He received mechanical ventilation and continuous sedation. One-gram ceftriaxone and antiepileptic drugs were initiated. Laboratory tests revealed renal dysfunction, but conservative treatment (no hemodialysis) was maintained. On the second day, the antimicrobial therapy was modified to include one-gram of ampicillin and 250 mg of acyclovir. A brain MRI revealed frontal, parietal and mesial bilateral temporal cortical and subcortical altered signals with restricted diffusion and similar abnormalities in the posterior thalamus, midbrain and cerebellar vermis, and no enhancement was noted. These findings were compatible with a diffuse encephalitis. Further CSF analysis (day 12 of the disease) revealed pleocytosis (98 cells/mm with 68% of lymphocytes and 12% of monocytes), high protein (161 mg%), normal glucose (81 mg%) and high adenosine deaminase level (47.9 international units (UI)/L, normal < 4.5 UI/L). Negative results were obtained for syphilis and the human immunodeficiency virus (HIV) antibodies and polymerase chain reaction for Mycobacterium tuberculosis, herpes virus types 1 and 2 were carried out. CSF and serum were positive for IgM antibodies to CHIKV (using the IgM antibody capture ELISA [MAC-ELISA] and commercial ELISA [Euroimmun, Lubeck, Schleswig-Holstein, Germany], respectively). A clinical deterioration of the patient was identified and despite the absence of sedative drugs, he remained in a coma and died on day 24 after onset of the illness.