Between 1981 and 1995, approximately 5 million people from either Mexico, Cuba, Central America, or South America immigrated to the United States. Some regional studies have suggested that as Hispanic immigrants become acculturated to American society, their risk of mental illness increases sharply. This study examined the lifetime risk of psychiatric and substance use disorders among U.S. Hispanic subgroups and the specific role of nativity, parental nativity, language preferences, and other sociodemographic characteristics as risk factors for these disorders. The study used the National Comorbidity Survey (NCS), a national probability sample of 8098 U.S. adults aged 15 to 54. Selected DSM-III-R psychiatric diagnoses were collapsed into eight categories. When compared with non-Hispanic whites, Mexican-Americans were less likely to have any psychiatric disorder. After multivariate adjustment, acculturation items predicted greater risk of having any DSM-III-R disorders for Mexican-Americans and "other" Hispanics and greater risk of having a substance abuse disorder for Puerto Ricans, among other significant relationships. The results suggest that there is likely to be an increasing prevalence of psychiatric and substance use disorders among Hispanics that may be attributable to increasing levels of acculturation among the more than 5 million recent immigrants from Latin America.