Smoking is a leading cause of morbidity and premature mortality in the United States. The relationship between tobacco smoking and several forms of cancer, heart disease, stroke, chronic lung disease, and other medical diseases is well recognized and accepted. Recent epidemiological studies are now focusing on the link between tobacco use and psychiatric diseases. Experts now suggest that in the differential diagnosis of "smoker," depression, alcohol dependence, and schizophrenia are highest on the list. Studies are also focusing on the role of secondhand tobacco exposure, either in utero or during childhood, in the risk of dual disorders. Prenatal exposure may alter gene expression and change the risk for a variety of life-long psychiatric diseases, e.g., ADD/ADHD, antisocial personality disorders, substance use disorders, and major depression. Considerable time and effort have been devoted to studying the link between smoking and depression and also schizophrenia. We will focus on less well-studied areas in tobacco use and psychiatric dual disorders (including eating disorders), prenatal and early childhood secondhand smoke (SHS) exposure, and the relationship to the genesis of these dual disorders.