OBJECTIVE: The goal of this study was to investigate associations between empirically defined dimensions of spirituality, personality variables, and psychiatric disorders in Vietnam era veterans. METHOD: One hundred pairs of male twins from the Vietnam Era Twin Registry were administered the self-report Spiritual Well-Being Scale and a pilot Index of Spiritual Involvement. Correlation analyses were supplemented with regression analyses that examined the relative influence of genetic and environmental factors on aspects of spirituality. RESULTS: Existential well-being was significantly associated with seven of 11 dimensions of personality and was significantly negatively associated with alcohol abuse or dependence and with two of three clusters of personality disorder symptoms. Associations between mental health variables and religious well-being or spiritual involvement were much more limited. CONCLUSIONS: Useful distinctions can be made between major dimensions of spirituality in studies of spirituality, religious coping, and mental health.