Objective: Demographic (i.e., age and years of education) and cultural (i.e., acculturation, amount of education outside the United States (U.S.), and English fluency) factors impact neuropsychological test performance in multiethnic individuals. To our knowledge, no study has investigated these factors using a quantitative measure of English language proficiency (ELP) in a multiethnic sample. The present study incorporated an ELP battery subtest to determine the best predictor of verbal and nonverbal neuropsychological test performance. Method: Participants consisted of 68 healthy adults (M Age = 36 years [SD = 13.6], 38% male, Hispanic [n = 8], Middle Eastern [n = 27], and Asian/Pacific Islander [n = 33]). All participants completed measures of acculturation, ELP (Woodcock Language Proficiency Battery-Revised, Reading Comprehension subtest), and a neuropsychological battery containing hypothesized verbal (Controlled Oral Word Association Test, Animal Naming, Boston Naming Test [BNT], and the Stroop Test) and nonverbal (Wisconsin Card Sorting Test [WCST], Rey-Osterrieth Complex Figure Test, Ruff Figural Fluency Test, and the Color Trails Test [CTT]) subtests. Results: Principal component analysis identified verbal (Animal Naming and BNT) and nonverbal (WCST and CTT) components. Hierarchical regression revealed that ELP predicted the verbal component over and above acculturation, education years obtained outside the U.S., and demographic factors (R2 change = .09, p < .01). However, only demographic factors (age and education) predicted the nonverbal component (R2 = .28, p < .01; all other p's>.20). Conclusion: Better performance on a quantitative measure of ELP is associated with better performance on verbal neuropsychological subtests after accounting for other cultural and demographic factors. This underscores the importance of quantifying ELP for understanding verbal neuropsychological performance in ethnically diverse individuals evaluated in English.