Guira Cuckoos (Guira guira) are cooperative breeders with joint nests, where several breeding and nonbreeding males and females remain in a cohesive unit through repeated breeding attempts within a single territory. We used nine microsatellite markers to analyze parentage and relatedness in a population of Guira Cuckoos in central Brazil, comprising 225 progeny from 51 breeding attempts. The Guira Cuckoos presented a variety of mating patterns, polygynandry and monogamy being the most common. We found low levels of extragroup fertilization, and cobreeding males and females within groups shared reproduction to some extent. Relatedness among group members varied. In some groups, adult males were more related to each other than expected by chance and, overall, males within groups were genetically more similar than background genetic relatedness. In addition, for some of the groups, males were more genetically similar than expected by chance in different years, which indicates some degree of male philopatry or possible joint dispersal by male kin. Male Guira Cuckoos were more likely to breed closer to their natal territories than females, a pattern of dispersal commonly found in birds. We also found that nonbreeding adult males had a higher number of nondescendent kin (chicks and embryos) in the nest than expected from background genetic relatedness, which implies that possible indirect reproductive benefits may have been a significant factor in the evolution of this breeding system.