Earlier use of tobacco in adolescence is associated with numerous adverse outcomes later in life. Although a number of studies have linked individual differences in affective functioning to adolescent smoking, these have relied primarily on self-report measures, and the contribution of different dimensions of affect to the onset of tobacco use during this period remains unclear. The current study examined these issues in a sample of 180 adolescents recruited from an ongoing prospective, longitudinal study examining emotional development. At approximately age 12, participants completed a questionnaire measure of affective temperament and took part in a family interaction task that was coded observationally to provide measures of dysphoric, aggressive, and positive behaviors. At 2 subsequent assessments, which took place approximately 2.5 years and 4 years after the initial assessment, participants completed a questionnaire measure of substance use. In total, 70 participants initiated smoking between the ages of 12 and 17. An earlier onset of smoking was predicted by more aggressive and less positive observed behavior during the interaction task, as well as lower levels of self-reported temperamental Effortful Control. There were no associations between dysphoric behaviors, or temperamental measures of negative affectivity or surgency and the onset of smoking. The findings add to a small body of literature demonstrating that behavioral components of affect can prospectively predict substance use in adolescence and suggest that different dimensions of affect show unique relationships with early substance use.