Objectives Examination of the relationship between military service and criminal conviction, and evaluation of its sensitivity through the use of two distinct study designs. Methods Data were collected on the conviction histories of a cohort of men convicted of a crime in 1977 in the Netherlands (n0678). The men were born between 1940 and 1964, and reached the age of military eligibility during an era when service was compulsory, although they could be classified as ineligible or exempt for a variety of reasons. Information on criminal conviction was collected from age 12 (the age of criminal responsibility) to calendar year 2003. The first study design-a quasiexperiment-uses panel methods and control variables to compare the risk of conviction among men who served in the military to all other men in the sample who did not serve in the military, irrespective of their reason for not serving. The second study design-a natural experiment-compares men who served in the military to men who, as a result of policies of the Dutch government, were exempt from service but otherwise would have served. For example, at various times, the Dutch government exempted an entire birth cohort from service, or exempted men through use of a lottery. Results In the quasi-experiment, military service reduced the odds of criminal conviction by 22% in each year of the post-service period (odds ratio00.78; p<.01). In the natural experiment, on the other hand, there was no relationship between military service and long-term conviction risk (odds ratio00.98). Follow-up analyses indicated that the results from the two study designs did not differ by crime type, nor were they age graded. There was suggestive evidence that military service actually worsened conviction risk among men who performed the worst on tests of military fitness (e.g., intelligence, language and mathematical skills). Conclusions Two study designs yield two different conclusions concerning the impact of military service on long-term conviction risk. However, the authors view the results from the natural experiment as authoritative, due to the success of this design in achieving superior balance between men who served in the military and men who did not serve. Therefore, the authors conclude that military service had no causal impact on criminal conviction in a sample of high-risk Dutch men. Qualifications of the study findings include the use of conviction data from official sources, the use of a sample of men who were all convicted of a crime at some point in their lives, and the study of military service which was compulsory rather than voluntary. Attention should also be paid to the different cultural and military context of the Netherlands compared to the United States.J Exp Criminol (2012) 8:135-164 DOI 10.1007/s11292-012-9140-