Despite slight variations in age of onset across ethnic groups, it appears that adolescents generally initiate substance use at an early age. Therefore, it is necessary to identify contributing factors that prompt early initiation, not only in ethnic populations but in White youth also. Members of some ethnic cultures, such as Hispanic/Latino have experienced drastic increased in substance prevalence rates, whereas prevalence rates for other youth populations, such as African-American have been consistent across time. This information stresses the need for additional research to better understand the societal/environmental influences that contribute to substance use. Several recommendations are presented in the area of treatment which include: more prevention efforts are needed for early age onset, pretreatment evaluations should assess for acculturation level of both youth and parent, and knowledge about acculturation level may be helpful in determining to what extent risk and protective factors common to particular ethnic groups may be relevant to the family. This paper reviews epidemiology and substance use patterns among four major ethnically diverse youth populations (i.e. Hispanic/Latino, African-American, Asian American/Pacific Islander, and Native American). The paper also highlights treatment implications and future research recommendations. References