Previous research has indicated that marriage contributes to desistance from crime. Two theories have been offered to explain this effect. This first, grounded in informal control theory, suggests that the marriage effect is a direct result of social bonds that tend to accompany marriage; the second contends that the effect is indirect and due to the impact of marriage on patterns of delinquent peer association. Using data from waves 5 and 6 of the National Youth Survey (NYS), this study re-examined the relationship between marriage, delinquent peer association, and desistance from marijuana use to determine which interpretation best explained the marriage effect. The data were divided into two samples: the total sample of individuals surveyed in waves 5 and 6 of the NYS (n=1,494), and the filtered sample of marijuana users who were single at the time of the wave 5 data collection (n=552). Using logistic regression analysis, the study found that while change in delinquent peer association was a powerful predictor of marijuana desistance, findings were also consistent with the control theory interpretation of the marriage effect. These findings highlight the need for additional longitudinal studies of desistance that examine variables derived from both control and differential association theories. Study limitations are also discussed. References, tables, appendix