Purpose: To identify predictors of the transition from experimentation to regular smoking in middle adolescence, late adolescence, and young adulthood. Methods: California and Oregon students completed self-report surveys assessing the following potential predictors of the transition to regular smoking from grades 8 to 10 (n = 2496), grades 10 to 12 (n = 2149), and grade 12 to age 23 years (n = 1534): demographic characteristics; smoking-related attitudes, behaviors and environment; other problem behaviors; academic orientation; parental bonding; and mental health. Huberized regression techniques, which adjust for weighting and clustering of observations, were used to determine the independent associations of the predictor variables on subsequent smoking status. Results: Risk factors for the transition to regular smoking during middle adolescence included being white, prosmoking attitudes, friend smoking, weak academic orientation, and less parental support. During late adolescence, being African-American was protective, whereas risk factors included prosmoking attitudes, drinking, non-intact nuclear family, and less parental support. Risk factors in young adulthood included younger age and prosmoking attitudes. Conclusions: Results point to several smoking-related attitudes, social influences, and behaviors that prevention efforts may target to curb the escalation of smoking. (C) Society for Adolescent Medicine, 2003.