Previous research has shown that ethnic background impacts scores on measures of psychological functioning. False positives and false negatives may be obtained as a function of cultural differences. This paper examines the Acculturation Rating Scale for Mexican Americans (ARSMA), an instrument that might be used clinically to augment interpretation of measures such as the Minnesota Multiphasic Personality Inventory. The ARSMA consists of 20 questions measuring preferences and behavioral tendencies on a five-point continuum from Mexican to Anglo orientation. Questions were selected to reflect five elements of acculturation: language familiarity and usage, ethnic pride and identity, ethnic interaction, cultural heritage, and generational proximity. The instrument was administered to 450 college freshmen, of whom 352 were Mexican-American according to surname and self-report. Confirmatory factor analysis evaluated the fit of the data to six alternative four-factor models extrapolated from previous research and theoretical expectations. The results suggest that the constructs measured by the ARSMA are substantially correlated, and that the measure may have a more parsimonious structure than that suggested by previous studies using less sophisticated methods. This paper contains 24 references and 7 statistical tables. (Author/SV)