A study was conducted to assess the effects of generational status on various measures of stigmatization, acculturative stress, and perceived social and interpersonal threat within the Mexican heritage population in the Southwest. The role of the fear of stigma by association, regardless of actual experiences of stigmatization, was investigated, including its relationships with acculturative stress, perceived threat, and social distancing. Exploratory analyses indicated that first generation Mexican Americans differed significantly from second generation Mexican Americans on the perception of Mexican nationals as ingroup members, the fear of stigma by association by Americans, and levels of acculturative stress. Additional analyses indicated that Mexican Americans with one parent born in Mexico and one in the United States held opinions and attitudes most similar to second generation Mexican Americans. Results from path analyses indicated that first-generation Mexican Americans were more likely than second-generation Mexican Americans to both see Mexican nationals as ingroup members and to be afraid of being stigmatized for their perceived association with them. Further, seeing Mexican nationals as in-group members resulted in less social distancing and lower perceived threat, but fear of stigma by association lead to greater perceived threat and greater acculturative stress. Implications for within- and between-group relations and research on stigma by association are discussed.