The purpose of this study was to examine associations between (a) self-reported reasons for and contexts of alcohol use and (b) high-intensity drinking (i.e., having 10+ drinks in a row in the past 2 weeks) among national samples of U.S. 12th grade students. Data were obtained from 16,902 students who reported any past 12-month alcohol use from nationally representative annual 12th grade student samples from 2005–2016. When asked about drinking behavior during the past 2 weeks, 72% reported consuming less than 5 drinks at most during 1 drinking occasion; 14% reported 5–9 drinks, 7% reported 10–14 drinks, and 7% reported 15+ drinks. Adolescent drinkers in all categories (<5, 5–9, 10–14, and 15+ drinks) endorsed “to have a good time” as the most prevalent reason for alcohol use, and “at a party” as the most prevalent context of alcohol use. However, high-intensity drinking was particularly likely among adolescents drinking for coping, compulsive use, and drug effect reasons, as well as those who enjoyed the taste. Having 15+ drinks (vs. 10–14 drinks) was particularly associated with compulsive use and enjoying the taste. The relative risk of any high-intensity drinking, and of higher levels of high-intensity drinking involvement, increased with the total number of reasons and contexts endorsed. Alcohol appears to serve a larger number of functions for high-intensity drinking adolescents than non-high-intensity drinking youth.