The study also evaluated whether group differences in exposure contributed to differences in prevalence. A cross-sectional community survey of lifetime adverse experiences and substance and psychiatric disorders was conducted between 1997 and 2000 in Miami-Dade County (Florida). A total of 1,083 former public school students between ages 19 and 21 years were interviewed. Drug dependence disorder was assessed by DSM-IV criteria using the Composite International Diagnostic Interview and a checklist of lifetime exposure to major and potentially traumatic experiences. Age at time of first occurrence was included. The results indicate that exposures to major and potentially traumatic experiences are commonplace among young people in South Florida. The African-Americans experienced more than 10 such events while the other three groups -- Cubans, Caribbean basin Hispanics, and non-Hispanic Whites -- averaged more than 7. This racial difference is a crucial dimension of the distinctive individual and social histories of African-Americans in this country. When death events were set aside, 28 of the remaining 33 events examined were found to be associated with significantly increased risk of drug dependence with temporal order, gender, ethnicity, and socioeconomic status controlled. For both genders and across all four ethnic categories, increases in exposure to adversity were significantly associated with increased risk for drug dependence. The rate at which increases in exposure were translated into increases in risk for drug dependence was dramatically lower among African-Americans than for the other groups. These results have demonstrated that cumulative adversity, both those distant in time and more proximal, contributes significantly to the prediction of drug dependence, demographic factors controlled. The role of cumulative adversity remains clearly observable with prior psychiatric disorders, attention deficit, and hyperactivity disorder (ADHD) and childhood conduct disorder held constant. The findings suggest that high levels of lifetime exposure to adversity are implicated causally in the occurrence of drug-dependence. 1 figure, 3 tables, 54 references