To relate exposure to televised youth smoking prevention advertising to youths' smoking beliefs, intentions, and behaviors. Methods. We obtained commercial television ratings data from 75 US media markets to determine the average youth exposure to tobacco company youth-targeted and parent-targeted smoking prevention advertising. We merged these data with nationally representative school-based survey data (n = 103 172) gathered from 1999 to 2002. Multivariate regression models controlled for individual, geographic, and tobacco policy factors, and other televised antitobacco advertising. There was little relation between exposure to tobacco company-sponsored, youth-targeted advertising and youth smoking outcomes. Among youths in grades 10 and 12, during the 4 months leading up to survey administration, each additional viewing of a tobacco company parent-targeted advertisement was, on average, associated with lower perceived harm of smoking (odds ratio [OR] = 0.93; confidence interval [CI] = 0.88, 0.98), stronger approval of smoking (OR = 1.11; CI = 1.03, 1.20), stronger intentions to smoke in the future (OR = 1.12; CI = 1.04, 1.21), and greater likelihood of having smoked in the past 30 days (OR = 1.12; CI = 1.04, 1.19). Exposure to tobacco company youth-targeted smoking prevention advertising generally had no beneficial outcomes for youths. Exposure to tobacco company parent-targeted advertising may have harmful effects on youth, especially among youths in grades 10 and 12.