From April 1981 to March 1982, 118 suspected clinically Japanese Encephalitis cases among children were admitted to two hospitals in Jakarta. Serological confirmation with H.I. and IAHA tests showed a 4-time increase against JE antigen in 25.4% cases and against Dengue antigen in 17% cases. Both diseases afflicted mainly children in the age group of 0-5 years. More severe symptoms and sequalae were found among JE cases then among Dengue Encephalitic Syndrome (DES) cases. The differential diagnosis for DES can be easily made if rash is present. The diagnosis of JE with WHO criteria were for 75% confirmed by the serological test. Out of 144 spinal fluid collected, four had CPE in LLCMK2 and two in PMK cell lines, further passages failed to demonstrate more CPE.