This study estimated the expected smoking duration for young smokers who have started recently. Data from National Health Interview Surveys were combined to model the ages at which smoking prevalence will decline to various percentages of the peak smoking prevalence for each successive birth cohort. Smoking-cessation ages were then estimated for the males and females born from 1975 through 1979. The median cessation age for those in this cohort who start smoking as adolescents is expected to be 33 years for males and 37 years for females. Thus, 50% of these adolescent males may smoke for at least 16 years and 50% of these adolescent females may smoke for at least 20 years, based on a median age of initiation of 16 to 17 years. Despite the decline in the median age of US smokers who quit, these data predict that smoking will be a long-term addiction for many adolescents who start now.