More than one-third of the approximately two million people entering publicly funded substance abuse treatment in the United States do not complete treatment. Additionally, racial and ethnic minorities with addiction disorders, who constitute approximately 40 percent of the admissions in publicly funded substance abuse treatment programs, may be particularly at risk for poor outcomes. Using national data, we found that blacks and Hispanics were 3.5-8.1 percentage points less likely than whites to complete treatment for alcohol and drugs, and Native Americans were 4.7 percentage points less likely to complete alcohol treatment. Only Asian Americans fared better than whites for both types of treatment. Completion disparities for blacks and Hispanics were largely explained by differences in socioeconomic status and, in particular, greater unemployment and housing instability. However, the alcohol treatment disparity for Native Americans was not explained by socioeconomic or treatment variables, a finding that warrants further investigation. The Affordable Care Act could reduce financial barriers to treatment for minorities, but further steps, such as increased Medicaid funding for residential treatment and better cultural training for providers, would improve the likelihood of completing treatment and increase treatment providers' cultural competence.