PURPOSE: To help clinicians and care systems determine the priority for tobacco counseling in busy clinic schedules, we assessed the lifetime health and economic value of annually counseling youth to discourage smoking initiation and of annually counseling adults to encourage cessation. METHODS: We conducted a microsimulation analysis to estimate the health impact and cost effectiveness of both types of tobacco counseling in a US birth cohort of 4,000,000. The model used for the analysis was constructed from nationally representative data sets and structured literature reviews. RESULTS: Compared with no tobacco counseling, the model predicts that annual counseling for youth would reduce the average prevalence of smoking cigarettes during adult years by 2.0 percentage points, whereas annual counseling for adults will reduce prevalence by 3.8 percentage points. Youth counseling would prevent 42,686 smoking-attributable fatalities and increase quality-adjusted life years (QALYs) by 756,601 over the lifetime of the cohort. Adult counseling would prevent 69,901 smoking-attributable fatalities and increase QALYs by 1,044,392. Youth and adult counseling would yield net savings of $225 and $580 per person, respectively. If annual tobacco counseling was provided to the cohort during both youth and adult years, then adult smoking prevalence would be 5.5 percentage points lower compared with no counseling, and there would be 105,917 fewer smoking-attributable fatalities over their lifetimes. Only one-third of the potential health and economic benefits of counseling are being realized at current counseling rates. CONCLUSIONS: Brief tobacco counseling provides substantial health benefits while producing cost savings. Both youth and adult intervention are high-priority uses of limited clinician time.