Next to Blacks, Mexican-Americans are the largest ethnic minority group among the visible opioid addict population in the United States. Although commonly grouped together with Puerto Ricans and other Spanish-speaking peoples under the rubric "Hispanic," Mexican-Americans have a unique culture and ethnohistory. In this report we review the clinical and research literature and present new data from studies of Mexican-American opioid users in San Antonio. Mexican-American addicts tend to use fewer classes of illicit drugs and are less likely to use stimulants and psychedelics than Whites or Blacks. Onset of daily opioid use occurs at an early age, typically around 20, yet first voluntary admission to treatment usually occurs later than it does for other ethnic groups. Mexican-American addicts tend to be arrested more frequently and spend significantly more years in correctional institutions, but there is also evidence that they spend more time voluntarily abstinent and employed during their careers. The duration of the career is prolonged, however, and typically exceeds 20 years. Mexican-Americans prefer individual to group treatment, and are especially unlikely to participate in traditional therapeutic communities and group psychotherapies. The Mexican-American client is the least likely to complete treatment without adverse termination. The literature seems unanimous in calling for more treatment of Mexican-American addicts by Mexican-American therapists, but we found little empirical outcome data which demonstrated that ethnic matching of therapist and client brings better results.