Examination of extensive data from field and laboratory studies indicates that prairie voles (Microtus ochrogaster) are socially monogamous and form pair-bonds. We used grid-trapping data from replicate populations of prairie voles living in 0.1-ha small mammal enclosures at 2 different initial densities to examine the extent to which opposite-sex adults captured together in the same live trap reflected social associations established from nest-use patterns and the probability that the pair produced offspring. Females classified as a resident at a nest that also included at least 1 resident male (male-female pairs or groups) were significantly more likely to be trapped with a male from the same social unit (64%) rather than a male from another social unit or a male wanderer (an animal not considered a resident at any nest site). On the other hand, females residing at a nest with no resident males were caught with wandering males significantly more often (84%) than with resident males from another nest. Finally, female wanderers were significantly more likely to be trapped with male wanderers (75%) than with resident males. A genetic analysis of parentage revealed that females were significantly more likely to have produced offspring with the male with which they were caught most frequently (80% of females) than to not breed with these males. None of these findings were influenced by density. Overall, the multiple-capture data were consistent with social monogamy and the relative frequency of male-female multiple captures were predictive of the likelihood of mating. However, although most females residing at nests with resident males bred with these males (84%), a similar percentage of these females also bred with at least 1 male that never resided in the same social unit as the female, suggesting that prairie voles are not genetically monogamous throughout their lives.