The hematophagous bug Triatoma brasiliensis (Neiva) is an important vector of Chagas disease in Brazil. We describe the mating behavior of this species in a comparative manner and analyze the effect of time elapsed since the first imaginal bloodmeal on motivation of males to mate, on female mate-rejections, and on overall mating frequency. We also evaluate whether females of this species copulate with several males in short time intervals, and we examine whether the duration of copulation may vary in the presence of other males compared with what is observed with isolated pairs. Age affected the motivation of males to perform mating attempts, whereas nutritional status affected the receptivity of females. Results showed that 70% of the females tested accepted copulating with three males over a period of 90 min, whereas the remaining 30% mated with at least two males. Mating duration in T. brasiliensis was prolonged in the presence of other males compared with observations of isolated pairs, and males of this species performed long postcopulatory associations only in the presence of other males, apparently as a mate guarding response to the presence of potential competitors.