This study investigated disparities in dual diagnosis (comorbid substance use and depressive/anxiety disorders) among US adults by nativity and racialethnic origin and socioeconomic, cultural, and psychosocial factors that may account for the observed disparities. The study drew on data from two waves of the National Epidemiological Survey on Alcohol and Related Conditions. Racialethnic categories included African, Asian/Pacific Islander, European, Mexican, Puerto Rican, and other Hispanic/Latino. Substance use and depressive/anxiety disorders were assessed per DSM-IV. A four-category measure of comorbidity was constructed: No substance use or psychiatric disorder; substance use disorder only; depressive/anxiety disorder only; and dual diagnosis. The data were analyzed using multinomial logistic regression. The prevalence of dual diagnosis was low but varied by nativity, with the highest rates among Europeans and Puerto Ricans born in US states, and the lowest among Mexicans and Asians/Pacific Islanders. The nativity and racialethnic effects on likelihood of having dual diagnosis remained significant after all adjustments. The limitations included measures of immigrant status, raceethnicity, and stress and potential misdiagnosis of mental disorder among ethnic minorities. This new knowledge will help to guide public health and health care interventions addressing immigrant mental and behavioral health gaps. This study addressed the research gap in regard to the prevalence and correlates of dual diagnosis among immigrants and racialethnic minorities. The study used the most current and comprehensive data addressing psychiatric conditions among US adults and examined factors rarely captured in epidemiologic surveys (e.g., acculturation).