Most studies of inbreeding depression have confounded levels of inbreeding of parents with those of offspring. We used 4 experimental groups of prairie voles (Microtus ochrogaster) in which both parents and offspring were noninbred, parents and offspring were inbred, or parents and offspring differed in their level of inbreeding. For each pair, we recorded latency to the production of the 1st litter, number of litters produced and number of young born in 120 days, litter weights from birth to weaning, and parental behavior. Noninbred parents produced more litters and young and showed shorter interlitter intervals than did inbred parents. Inbred offspring weighed less at birth and weaning. We found no significant differences in parental behaviors among groups. Our results demonstrate that inbreeding depression occurs in prairie voles, and that it may be influenced more by physiological changes in inbred parents or young than by behavioral deficiencies in inbred parents. However, larger sample sizes could reveal that parental behavior does have an effect.