To assess effects of maternal separation on later aggressive and reproductive behaviors, male Sprague-Dawley pups were separated from their mothers every other day for 8 h (long-term separation; LTS), 4 h (short term separation; STS), or 0 h (no separation; NS) from post-natal day 2 through 20. Maternal behaviors, including lactation performance, nest building, grouping, and hovering over pups were measured during the separation period. At maturity, aggressive behavior of male subjects was assessed. Subjects were also mated to novel females and reproductive outcomes measured. It was hypothesized that male pups periodically separated from their mothers would demonstrate increased aggression and decreased reproductive success as adults. Contrary to expectations, maternal separation did not affect later adult aggressive behavior or reproductive outcomes. Additional studies examining the role of the neonatal environment in shaping subsequent male behavior are needed.