The objective of this study was to describe the seasonal distribution of malaria vectors in Machadinho d'Oeste, Rondônia State, Brazil. The study was based on data from the Brazilian National Health Foundation (FUNASA) for the period from April 1993 to November 1994. A total of 97 field visits were conducted, and 93 intradomiciliary and 95 peridomiciliary collections were performed. The most frequently captured species in both the intra- and peridomiciles was Anopheles darlingi, followed by Anopheles triannulatus, among other species. Only An. darlingi was captured throughout the study period, and it was more abundant during the transition from the dry to the rainy season and vice versa. The elaboration of scientific studies based on secondary entomological data from FUNASA has been reinforced, since these results are comparable to those from the literature, taken from studies using primary data.