Objective: The objective of this study was to assess whether comparisons of longitudinal smoking trajectories predict differences in symptoms of ADHD in adults. Method: Participants were interviewed 7 times between 14 and 43 years of age. ADHD symptoms at outcome were assessed with the World Health Organization ADHD Self-Report Scale. Bivariate and multivariate linear regression analyses assessed the associations between the trajectories of smoking and ADHD symptoms. Results: The multivariate analysis (R ² = .12) indicated that compared with being nonsmokers, the probability of being in the heavy/continuous group (standardized regression coefficient [SRC] = .17, p < .01) and in the late starter group (SRC = .11, p < .05) were significantly associated with adult ADHD symptoms. Conclusion: Longitudinal smoking patterns were associated with ADHD symptoms in adults. Chronic smoking jeopardizes both physical health and the ability to fulfill adult roles as employees, family members, and friends. Smoking cessation in adolescence may lessen the likelihood of ADHD symptoms in adulthood.