Understanding the evolution of cooperative breeding systems remains a central issue in evolutionary biology. In this context, molecular tools have contributed greatly toward understanding kinship patterns within groups and resolving long-standing issues regarding mating systems and parentage. We used such molecular tools to examine patterns of kinship in the Campo Flicker (Colaptes campestris campestris), a facultative cooperative breeder, to answer questions concerning its mating system and patterns of reproductive skew. Genetic analysis revealed that the species is predominantly monogamous in both cooperative groups and socially monogamous pairs, but in several cooperative groups auxiliary females contributed eggs to the nest. In contrast, within groups direct reproduction by auxiliary males was rare. We observed no cases of extra-group paternity but detected cases of quasi-parasitism in socially monogamous pairs. Levels of relatedness within groups were high; auxiliaries of both sexes were often offspring or siblings of the primary breeding pair but were sometimes unrelated to the breeding pair. The structural genetic complexity of groups and high intragroup relatedness generate a social system in which cooperation among group members coexists with competition for opportunities to breed.