Although the military is one of the largest employers and educators of young adults in the country, scant research has focused on the short-term and long-term effects of military experience. The field of criminology, in particular, has thus far failed to examine the impact of military service on criminal behaviors. As such, the author analyzed two cohort studies, Wolfgang’s 1945 Philadelphia birth cohort study and Shannon’s 1949 Racine, WI, birth cohort study, to discover the effect of military service on criminality. Approximately half of the men in the Philadelphia participants served on active duty in the military, while almost 40 percent of the Racine participants had active military duty. Criminal behavior was measured by police contacts for both cohorts; a separate variable was created for police contacts for violent offenses. Results of logistic regression models and negative binomial models indicate that, overall, military service reduced later offending behavior. However, military service did not significantly reduce the probability of engaging in later violent offenses. Limitations of the study include the fact that the cohort data did not indicate whether the participants spent time in combat, which may function as a critical variable in terms of later criminality, especially violent criminality. The main limitation of the study, however, rests in the inability to capture the mechanism responsible for the reduction in criminality that has been attributed to military service. To further extend the analysis, future research should utilize the life course perspective to better understand the relationship between military service and criminality. Tables, references