We compared the effects of daily long (3 h), brief (15 min) or no maternal separation (LMS, BMS, NMS) on postnatal days 2-14 on maternal behavior, aggression and anxiety levels during lactation in adulthood. Animals subjected to LMS received less maternal grooming than animals subjected to BMS. Maternal behaviors, including nursing, pup-grooming (PG) frequency and proportion of total grooming (PG+self-grooming) and nest-building during the immediate postpartum period and on postpartum days 2 and 5 were lower in dams with LMS experience compared to dams with BMS experience. LMS dams attacked male rats placed in their home cages less quickly and less often than did BMS or NMS dams. LMS dams also exhibited more anxiety than BMS dams in the elevated plus maze test. Thus, maternal separation during the postnatal period (or associated changes in the amount of maternal grooming received) affected subsequent adult maternal behavior, aggression and anxiety. The mechanism for this remains to be discovered, however, it seems likely to involve alteration of the development of oxytocin receptors in the brain.