Sensation seeking has been identified as a significant risk factor for adolescent alcohol use. Little is known, however, about the process by which sensation seeking impacts heavy alcohol use. The current study used structural equation modeling (SEM) to examine the relationships among sensation seeking, age of drinking initiation, and heavy alcohol use in a sample of high school seniors (N = 221). Results support age of drinking initiation as a mediator of the relationship between sensation seeking and heavy alcohol use. Implications include providing personality-targeted prevention to adolescents who display sensation-seeking traits to delay drinking initiation among these students.