During the months of September 1993 through February 1994, an outbreak of hemorrhagic fever occurred in the city of Jayapura, the provincial capital of Irian Jaya, Indonesia. Seventy-two patients (age range = 1-41 years) with suspected dengue hemorrhagic fever (DHF) were enrolled into the outbreak investigation conducted during October-November 1993. The pediatric patient population consisted of 36 individuals ages 1-12 years of age with a similar male to female ratio. From clinical histories obtained from the children diagnosed with DHF (n = 23), the predominant complaints were fever (100%), headache (96.7%), vomiting (47.8%), abdominal pain (39.1%), back/bone pain (39.1%), cough (39.1%), sore throat (21.7%), convulsions (17.4%), and eye pain (13.0%). Clinical findings of the same pediatric patients included a positive tourniquet test result (100%), thrombocytopenia (100%), hemoconcentration (100%), skin petechiae (43.5%), epistaxis (39.1%), and maculopapular rash (26%). All four of the children diagnosed with DHF grade IV had hepatomegaly, pleural effusion, ascites, cold perspiration, and confusion. Serologic data demonstrated that a majority (46 of 70, 68.7%) of the individuals assessed did not have significant levels of IgM specific for dengue viruses at the time of their admission. However, the nine successful dengue virus isolations were only from these serononreactive cases (19.6%). From the other patients assessed, 11.4% had a primary (or first exposure) serologic response to dengue virus antigen (predominantly IgM); 17.1% had a secondary (or subsequent exposure) serologic response to the same dengue antigens (predominantly IgG response) and 5.7% (four adults) had indeterminate serologic data that could not differentiate between reactivity to dengue or Japanese encephalitis virus antigen preparations. Virus culture of blood samples produced nine dengue virus isolates: DEN- 1 (2), DEN-2 (1), and DEN-3 (6). Japanese encephalitis and influenza viruses were not isolated from blood and pharyngeal specimens, respectively, from any of the patients. Thus, this first reported outbreak of DHF in Irian Jaya, Indonesia was found to be attributed to dengue viruses types 1, 2, and 3.