Prairie voles (Microtus ochrogaster) exhibit a monogamous mating system characterized by long-term pair bonds between mates. The purpose of this study was to examine the effect of cohabitation time and sexual experience on the development of pair bond formation in female prairie voles. Females that were allowed to cohabit for 24 hr or more, with or without mating, exhibited a strong social preference for a familiar partner versus a strange male. Females that cohabited and mated for 6 hr showed strong preferences for a familiar partner, while cohabitation for less than 24 hr, without mating, did not result in preferences for the familiar male. These results indicate that mating was not essential for partner preference formation; however, preferences developed more rapidly when mating occurred.