The purpose of the present study was to examine between- and within-person relationships among protective behavioral strategies (PBS), alcohol consumption, and related negative consequences during the 21st birthday week. Participants for the present study included undergraduate college students (n = 1,028) who turned 21 during three academic quarters at a large public northwestern university in the United States. Students completed a Web-based survey that comprised measures of 21st birthday PBS, alcohol consumption, and alcohol-related negative consequences. Between-person findings indicated that participants who used more manner of drinking PBS and fewer serious harm reduction PBS consumed fewer drinks and reached lower BACs. Results also showed that participants who used a greater number of limiting/stopping PBS and who used more manner of drinking PBS experienced fewer negative consequences. Within-person findings demonstrated that on days when participants used more limiting/stopping PBS, fewer manner of drinking PBS, and more serious harm reduction PBS than average they also consumed more drinks and reached higher BACs. When examining negative consequences, within-person results showed that on days when participants used more limiting/stopping PBS, fewer manner of drinking PBS, and more serious harm reduction PBS than usual they experienced more negative consequences. Discussion focuses on clarification of the association between PBS and drinking and implications for preventive interventions. (PsycINFO Database Record (c) 2012 APA, all rights reserved)