This study examined the measurement equivalence of the K6 across diverse racial/ethnic and linguistic groups in the U.S. differential item functioning analyses using item response theory were conducted among 44,846 U.S. adults drawn from the California Health Interview Survey. Results show that four items ("nervous," "restless," "depressed," and "everything an effort") varied significantly across races/ethnicities and four items ("nervous," "hopeless," "restless," and "depressed") varied significantly across languages. In additional effect size analyses designed to separate effects of race/ethnicity from language, the structure of the White English group was substantially different from both the Hispanic/Latino English group and Hispanic/Latino Spanish group, whereas the Hispanic/Latino Spanish group was not different from the Hispanic/Latino English group. The findings suggest that there was evident measurement nonequivalence in the K6 among racially/ethnically and linguistically diverse adults and that the observed nonequivalence in the K6 appears to be driven by language rather than race/ethnicity.