A suspected epidemic of unknown etiology was investigated in April/May 1996 in the remote jungle highlands of easternmost Indonesia. Trend analysis demonstrates the area-wide occurrence of a major respiratory infection outbreak in November 1995 through February 1996. The monthly mean rate of respiratory infection episodes for the peak outbreak months (2,477 episodes/100,000 persons) was significantly higher (P< .0001) than for the 34 months leading up to the outbreak (109 episodes/100,000 persons). Notable were the high attack rates, particularly among adults: 202 episodes/1,000 persons aged 20-50 years in one community. Excess morbidity attributed to the outbreak was an estimated 4,338 episodes. The overall case-fatality rate was 15.1% of outbreak cases. Laboratory evidence confirmed the circulation of influenza A/Taiwan/1/86-like viruses in the study population, and high hemagglutination inhibition titer responses were indicative of recent infections. Historical documents from neighboring Papua New Guinea highlight the role of influenza A virus in repeated area outbreaks.