We compared morphology of internal reproductive anatomy and genitalia among 10 species of North American Anthocoris (Hemiptera: Heteroptera: Anthocoridae). Reproductive structures of males, including internal reproductive organs (testes, seminal vesicles, ejaculatory bulb, phallus), the paramere, and the endosoma, were found to vary in size, shape, and appearance among the 10 species, although with similarities among species within some groupings. All species except Anthocoris bakeri Poppius have two testicular follicles per testis; A. bakeri has five to seven follicles per testis. In seven of the 10 species, a longitudinal groove was found to be present on the paramere; we believe this groove functions to guide the male's intromittent organ as it enters the female during copulation. Variation among species in morphology of the male's inflated endosoma included differences in length, presence or absence of looping, and in presence of spinulate, dentate, or tuberculate projections. The summary presented here is the first description of the endosoma for any species of Anthocoris. We observed substantial variation among species in length of the female's copulatory tube (i.e., the organ which receives the male's intromittent organ), although again with some similarities among certain groupings of species. Variation in length of the female's copulatory tube parallels variation in length of the male's endosoma, which suggests that morphology of genitalia within this genus has coevolved between sexes.