This study identifies longitudinal psychiatric trajectories of 934 adult individuals entering chemical dependency treatment in a private, managed care health plan and examines the relationship of these trajectories with substance use (SU) outcomes. The authors apply a group-based modeling approach to identify trajectory groups based on repeated measures of psychiatric severity for 9 years and identify four distinct groups. Results of multivariate logistic generalized estimating equation models find an association between psychiatric trajectories and long-term SU. Older cohorts and life course measures of marital status and employment status as individuals changed over time are related to drug and some alcohol outcomes. (Contains 2 figures and 4 tables.)