Social norms theories hold that perceptions of the degree of approval for a behavior have a strong influence on one's private attitudes and public behavior. In particular, being more approving of drinking and perceiving peers as more approving of drinking, are strongly associated with one's own drinking. However, previous research has not considered that students may vary considerably in the confidence in their estimates of peer approval and in the confidence in their estimates of their own approval of drinking. The present research was designed to evaluate confidence as a moderator of associations among perceived injunctive norms, own attitudes, and drinking. We expected perceived injunctive norms and own attitudes would be more strongly associated with drinking among students who felt more confident in their estimates of peer approval and own attitudes. We were also interested in whether this might differ by gender. Injunctive norms and self-reported alcohol consumption were measured in a sample of 708 college students. Findings from negative binomial regression analyses supported moderation hypotheses for confidence and perceived injunction norms but not for personal attitudes. Thus, perceived injunctive norms were more strongly associated with own drinking among students who felt more confident in their estimates of friends' approval of drinking. A three-way interaction further revealed that this was primarily true among women. Implications for norms and peer influence theories as well as interventions are discussed.