The Marion County Youth Survey was a 12-wave panel study of a base sample of 1,227 sophomore males from the high schools in Marion County, OR, beginning in 1964. The intent of the study was to conduct a longitudinal investigation into the development of and changes in delinquent behavior. Data were collected from the respondents through age 30. With reference to military service, the study differentiated youth who served in the military from those who did not, differentiated members of the armed forces into those who served in Vietnam and those who did not, and differentiated those who experienced combat while in Vietnam from those who did not. The dependent variables were measured by answers to questions regarding patterns of alcohol and marijuana use. Arrest records were obtained from self-reports and through systematic record checks. Respondents' arrests while in the military were included. Because the data were collected before, during, and after the respondents' entrance into the military, the study identified whether substantive distinctions between individuals existed before they entered the military. The study found that compared to the respondents who did not serve in Vietnam, service in Vietnam accelerated drug use above and beyond the general developmental trend to such a degree that service in Vietnam was indirectly associated with overall higher levels of arrest frequency. Thus service in Vietnam had a general deleterious effect on the life-course trajectories of veterans, because it exposed them to and embedded them in drug use; this in turn led to increased arrests over their life-course. 4 tables, 11 notes, and 57 references