Use of marijuana and alcohol among current college students (N = 1101) was compared to the perceptions and use of entering freshmen (N = 481) surveyed before the start of classes. Entering freshmen significantly misperceived campus norms for marijuana use, over-estimating that almost every student used in the last 30 days, p less than 0.001. Perceptions of alcohol use were relatively accurate. These discrepancies in perception could account for why 40.5% of entering students perceived the campus atmosphere to be promoting marijuana use, whereas only 16.2% perceived the campus atmosphere to be promoting alcohol use. How these misperceptions of social norms might be influenced by the reputation of the campus-and how this might affect potential applicants and enrolled students' behaviors are discussed.