Implicit race/ethnic prejudice was assessed using Spanish- and English-language versions of an Implicit Association Test that used Hispanic/Anglo first names and pleasant/unpleasant words as stimuli. This test was administered to a consecutive sample of Mexican American adults residing in the Rio Grande Valley region of Texas of whom about two-thirds chose to be tested in English and one-third preferred Spanish. Participants were mostly female (73%) with a mean age of 32 years and mean education of 13 years. Among 83 participants, 43% demonstrated in-group implicit prejudice while 26% showed out-group implicit prejudice toward Anglos. There was a significant negative correlation between family values (familism and filial piety) and implicit race/ethnic prejudice scores but no significant association was found between implicit race/ethnic prejudice scores and acculturation or skin tone. Results contribute to the ongoing controversy regarding the validity of implicit race/ethnic prejudice, supporting the concept that societal not individual prejudices are being measured. (Contains 1 table.)