An extensive outbreak of dengue fever and dengue hemorhagic fever occurred in the city of Palembang, South Sumatra, Indonesia from late 1997 through March/April 1998. All surveyed administrative areas (kelurahan) in Palembang were found to be 'permissive' for dengue virus transmission; and all areas that had Aedes (subgenus Stegomyia) larval mosquitoes in abundance experienced increased cases of DHF during the epidemic. The Aedes House Index (HI) for combined Aedes aegypti and Aedes albopictus was recorded every 3 months before, during, and after the epidemic. Ten surveyed sentinel sites (October-December 1997) immediately preceding the epidemic peak had a combined HI of 25% (range 10-50.8%). Entomological surveys during the peak epidemic period (January-April) showed a combined HI of 23.7% (range: 7.6-43.8%). Kelurahans with the highest numbers of reported dengue cases had an HI exceeding 25%; however, there was no discernable relationship between elevated HI and increased risk of DHF incidence. Despite the unusual climatic conditions during late 1997 created throughout the region by the El Niño Southern Oscillation (ENSO), the house indices during both wet and dry months remained above 23% for the 4 quarterly (3-month) periods surveyed in the second half of 1997 and first half of 1998. Rainfall returned to near normal monthly levels shortly before the reported increase in human cases. However, mean ambient air temperatures continued above normal (+0.6 to 1.2 degrees C) and were sustained over the months leading up to and during the epidemic. Evidence suggests that an ENSO-driven increase in ambient temperature had a marked influence on increased virus transmission by the vector population. We explore the apparent associations of entomological and climatic effects that precipitated the epidemic before the influx of reported human cases.