The purpose of this 2-wave longitudinal study was to specify, test, and evaluate an actor–partner interdependence model (APIM) with young adult marital dyads to test husbands’ and wives’ mutual influences on each other’s substance use. Prospective data were collected from young adults and their spouses at baseline and 5 years later. Data from 237 dyads were used to test spouses’ interdependence on alcohol use, alcohol problems, and marijuana use with the APIMs. Marital partners had significant effects on each other’s substance use, though the patterns were different contingent on the outcome referenced. Husbands’ alcohol use significantly predicted wives’ alcohol use and alcohol problems. Wives’ alcohol use and marijuana use significantly predicted husbands’ alcohol use, alcohol problems, and marijuana use. For these young adult dyads, partner influences were indicated for both spouses, but more pervasive influences were indicated from wives-to-husbands than the reverse.