The findings indicate that SUDs among adult Latinos in the United States are associated with the following features of social assimilation: the context in which adult Latinos prefer to use the English language and transformations in family and social-network relationships, which differ in important ways between Latino men and women. The study found that preference for using the English language within the family, rather than self-reported proficiency in the English language, was a more significant proxy for social assimilation in relation to the outcome of risk for SUDs. SUDs were positively associated with problematic family relations of Latino men, but not for Latino women; and SUDs among Latino women were positively associated with more frequent interactions with friends, but not for Latino men. These findings clearly show that Latino women and men with SUDs have different relational patterns with family and friends that merit continued attention in etiological, services, and treatment research. The Latino sample of the NLAAS study was a nationally representative sample of 2,554 Latinos 18 years old and older that consisted of individuals who identified themselves as Mexican-American or having a family of origin from Puerto Rico, Cuba, or other Latin country. Lifetime and last-year prevalence rates of SUDs were assessed with the diagnostic interview of the World Mental Health Survey Initiative. Proficiency in the English language and contexts in which it was used were determined by survey questions, as were the characteristics of interactions with family members and friends. 6 tables and 83 references