The mating behavior of the sand fly, Lutzomyia longipalpis, was studied under laboratory conditions. Male sand flies landed on the bodies of anesthetized mice, where they exhibited leklike displays such as wing fanning, parading, and aggression. Lek behavior was more frequent in older males, and dominance hierarchies were established. Male sand flies at leks copulated more frequently than male sand flies at other locations in the cage. Females mated by older males produced more eggs than did females mated by younger males; however, there was no difference in the number of larvae produced.