The research resulted from recognition that adolescents’ estimates of their peers’ smoking prevalence could influence their own smoking behavior, although how they formed these estimates or what factors influenced their accuracy was unclear. The data came from a representative sample of California youth in 8th grade and came from 68 schools in 18 California counties randomly selected within 4 sampling strata during the 1996-97 school year. A total of 4,296 of the 5,870 sampled students completed the questionnaires. Results revealed that best friends’ smoking accounted for the largest proportion of the variance in the prevalence estimate. Female gender, the actual prevalence of smoking in the student’s school, perceptions of smoking on television, perceived access to cigarettes, low academic performance, cigarette offers, and ethnicity were also significant correlates of the variance in prevalence estimates. The model’s variables accounted for 23.8 percent of the variance in smoking prevalence estimates. The analysis concluded that peers appear to be adolescents’ greatest source of information regarding smoking prevalence and that prevention interventions should demonstrate to adolescents that their perceptions of their peers’ smoking prevalence tend to be inflated, especially if they have close friends or schoolmates who smoke. Tables and 12 references