This study was undertaken to examine differences in caffeine and nicotine use between the psychiatric population and the addicted population in a private psychiatric inpatient facility. Eighty-six patients on an adult addictive disease inpatient unit and 80 patients on an adult psychiatry unit in a private psychiatric hospital were interviewed with regard to their use of nicotine and caffeine. In addition, demographic information and primary diagnoses were obtained from the psychiatric admission assessment in the medical record as listed by the admitting psychiatrist. Although there was little difference in psychiatric patients vs. chemically dependent patients with regard to the percentage of caffeine users, the chemically dependent individuals drank more coffee, soft drinks, and tea. A much greater percentage of the chemically dependent individuals also smoked cigarettes, although not in a greater amount than the psychiatric patients who smoked. Because group assignment was not random, ordinary least squares (OLS) regression analyses were conducted to determine the independent associations of age, sex, education, and treatment population in predicting levels of caffeine and tobacco use. Even after controlling for demographic differences between the two samples, chemically dependent patients still reported higher levels of daily caffeine and tobacco use than patients on the general psychiatric unit.