Many life course studies are based on a few cohorts of individuals born in the early part of the 20th century. Despite the significance of military service in the life course, few studies have addressed the consequences of military service on offending trajectories. This study explores the relationship between military service and patterns of offending in three cohorts of men. Analyses examine both the impact of military service as well as the potential period effects of service during different periods of the Vietnam War. Results suggest that between-individual differences in military service significantly affect criminal behavior. However, the specific direction of the effect depends on when during the Vietnam era these men entered the military. Implications of these results are discussed.