In this study, a total of 17 adult patients (>> or =18 years old; 12 male, 5 female) with encephalitis followed up in neurology and infectious diseases clinics of Trace University Hospital between the years 2000-2005 were retrospectively analyzed. The most common signs and symptoms were confusion (n: 13; 76.4%), nausea and vomiting (n: 13; 76.4%), disorientation (n: 12; 70%), fever and headache (n: 11; 64.7%), amnesia (n: 10; 58.8%), convulsions (n: 9; 52.9%), agitation (n: 7; 41%), dysphasia and aphasia (n: 6; 35.2%), nuchal stiffness (n: 5; 29.4) and focal neurological signs (n: 1; 5.8%). Six of the patients were admitted to the hospital during summer, six during winter, four during spring and one during autumn. Eleven (64.7%) of the patients had electroencephalographic signs compatible with encephalitis. Encephalitis related signs were detected in 83.3% (10/12) of the patients by cranial magnetic resonance imaging and in 58.3% (7/12) by computerized tomography. Cerebrospinal fluid (CSF) examination revealed low glucose levels in 17.6% (3/17), high protein levels in 47% (8/17) and increased white blood cells with a predominance of lymphocytes in 41.2% (7/17) of the cases. CSF findings were within normal limits in 23.5% (4/17) of the patients. Empirical acyclovir treatment was given to all patients. One patient died at the acute phase of the infection while all the other 16 recovered. Since none of the CSF samples yielded bacterial growth, all of the patients were diagnosed as viral encephalitis. However, no investigation was performed to identify the viral etiology and this was the major limitation owing to the inadequacy of laboratory facilities during the study period and/or unawareness of the physicians about viral identification methods.