The present paper offers preliminary evidence for a hierarchical organization of normative social influences on 21st birthday drinking. In recent years, 21st birthday celebratory drinking has received increasing attention, due largely to the propagation of dangerous and sometimes fatal drinking traditions, such as attempting to drink one shot for each year of life, sometimes in a single hour (Hembroff, Atkin, Martell, McCue, & Greenamyer, 2007; Neighbors, Spieker, Oster-Aaland, Lewis, & Bergstrom, 2005; Rutledge, Park, & Sher, 2008). Intervention strategies designed to curb dangerous 21st birthday drinking have incorporated social norms components and have been met with varying degrees of success (Hembroff et al., 2007; Lewis, Neighbors, Lee, & Oster-Aaland, 2008; Neighbors, Lee, Lewis, Fossos, & Walter, 2009; Smith, Bogle, Talbott, Gant, & Castillo, 2006). A better understanding of the relative influence of social norms on 21st birthday drinking may offer practical suggestions for more effective interventions. (Contains 2 tables.)