Motivational interviewing (MI) is a counseling style that has been shown to reduce heavy drinking among college students. To date, all studies of MI among college students have used a format that includes a feedback profile delivered in an MI style. This study was a dismantling trial of MI and feedback among heavy-drinking college students. After an initial screen, 279 heavy-drinking students were randomized to (a) Web feedback only, (b) a single MI session without feedback, (c) a single MI session with feedback, or (d) assessment only. At 6 months, MI with feedback significantly reduced drinking, as compared with assessment only (effect size = .54), MI without feedback (effect size = .63), and feedback alone (effect size = .48). Neither MI alone nor feedback alone differed from assessment only. Neither sex, race or ethnicity, nor baseline severity of drinking moderated the effect of the intervention. Norm perceptions mediated the effect of the intervention on drinking. MI with feedback appears to be a robust intervention for reducing drinking and may be mediated by changes in normative perceptions.