This paper examines how membership in a highly concentrated Vietnamese-American community affects the drug and alcohol use of Vietnamese-American secondary school students. It suggests that research on adolescent substance abuse has had a tendency to concentrate on the family environment and the peer group. For this ethnic group, however, the present study finds that involvement in the ethnic community has a strong negative effect on drug and alcohol abuse, both directly and indirectly, through lessening the likelihood that adolescents will have substance-abusing friends. Vietnamese language use is found to be an especially influential aspect of ethnicity. It is suggested that research on adolescent substance abuse should place more emphasis on community-level explanations, such as the effect of ethnic and other sorts of social groups that surround individuals and families.