This is the first of a series on the Triatominae (Hemiptera. Reduviidae) of the State of Bahia, Brazil. Surveys were made, of 889,972 dwellings in 11,04s localities of the State and 33,588 bugs were collected. Four genera and eighteen species of Triatominae were identified, as follows. Triatoma bahiensis Sherlock & Serafim, 1967 is here considered to be a synonym of subspecies of T. pessoai Sherlock & Serafim, 1967. Other subspecies or races of other Triatominae have been encountered in Bahia and will be considered fully elsewhere. Panstrongylus megistus (Burmeister, 1835) is more abundant in the littoral areas with tropical climate, high humidity and broad-leaved forest vegetation. P. megistus is considered to be the most important vector of Chagas Disease in the State of Bahia. T. brasiliensis Neiva, 1911 is principally found in areas with an arid climate and xerophilic vegetation. It was also found in some areas with tropical humid climate, where it maybe a different race. Some specimens were also caught in areas with a cooler climate and vegetation of moist broad-leaved forest. The spread of T. brasiliensis to this area is considered to be due to human agency. T. iniestans Klug, 1834, once limited in Brazil to temperate areas south of the 16th parallel, has been spreading northward through areas with diverse climate characteristics, possibly due to accidental means. T. sordida (Stal, 1859) was found to have a riverain distribution in areas with dry climate. T. rubrofasciata (e Geer. 1773) is limited to two old colonial ports in the State. Years ago it was quite abundant in these places. Improvements in sanitary conditions in recent years probagly account for the present scarcity of ihis species in both localities. The following species were found in small numbers and in limited areas: P. diasi (Pinto & Lent), P. geniculatus (Latreille), P. lutzi (Neiva & Lent), T. costalimai Verano & Galvao, T. lenti Sherlock & Serafim, T. maculata Erickson, T. melanocephala Neiva & Pinto, T. pessoai Sherlock & Serafim. T. petrochii Pinto & Barreto, and T. tibiamaculata Pinto. A single specimen of Rhodnius neglectus Lent, 1940 was caught, for the first time, in a house in a dry area of the northwest part of the State. Of the genus Psamolestes, only P. tertius Lent & Juberg, 1965 was found all over the State. This species was restricted to suitable bird nests, which are its normal habitat.