The article is based on information from the 1991 supplementary Drug and Alcohol Use Data File, which examined the self-reported substance use behaviors of approximately 21,000 adults aged 18-44. Findings indicate that immigrants to the United States in the late 20th century were less likely to use alcohol and other drugs than were native born citizens. Findings also suggest assimilation processes by which exposure to mainstream American society leads to patterns of alcohol and illicit drug use among long term immigrants approximating that of the native born population. The patterns of substance use observed among immigrants, however, were not consistent with acculturative stress mechanisms. The article presents an overview of the research literature concerned with this topic. Limitations to the study include use of cross-sectional survey data; reliance on self-reported measures of substance use behaviors; reliance on length of stay in the host country as a proxy indicator of acculturation; and findings were specific to the experiences of immigrants arriving in the United States during the late 20th century and could not be generalized to other countries or to the experiences of immigrants who entered the United States during earlier migration waves. Tables, references