We present a prospective case-control study of 27 serologically confirmed dengue hemorrhagic fever (DHF) patients with severe central nervous system symptoms. Dengue associated encephalopathy accounted for 0.5% of 5,400 patients admitted with DHF. The mortality rate among children with encephalopathy was 22%, with the survivors experiencing a complete recovery. Liver enzymes and bilirubin were significantly elevated in the study group. In analysis of the cerebrospinal fluid (CSF), reverse transcriptase-polymerase chain reaction revealed dengue-3-specific RNA in one evaluated case. Dengue-specific immunoglobulin M was detected in CSF in 14 of 22 assessable patients, indicating a localized infection. Magnetic resonance imaging scans showed cerebral edema in the majority of patients, although encephalitis-like changes were less common. There was an equal distribution of primary and secondary infections. On the basis of previous reports and of the findings of our study, DHF probably encompasses an expanding clinical spectrum that infrequently involves encephalitis due to a direct neurotropic effect of dengue virus.