DIAGNOSTIC MARKERS OF LANGUAGE IMPAIRMENT IN BILINGUAL ADULTS PROJECT SUMMARY Aphasia, which refers to language impairment following focal or degenerative brain injury, has a debilitating effect on a person’s quality of life due to its social, emotional and financial repercussions. A significant proportion of persons with aphasia are bilingual, given that nearly one-fifth of the U.S. population and over one-half of the world’s population is bilingual. The overlap in language behaviors between bilinguals of varying proficiency and persons with aphasia makes the diagnosis of bilingual aphasia particularly challenging. Yet, there are hardly any psychometrically valid diagnostic instruments to diagnose aphasia and differentiate it from the language variation seen across bilinguals. Over two-thirds of clinicians in the U.S. report being unprepared to assess bilingual adults due to unavailability of valid diagnostic tools and insufficient understanding of bilingual language disorders. The proposed research represents the first systematic psychometric investigation of clinical language measures in English for Spanish-English speaking bilingual adults across multiple language domains. The project will establish language measures, population norms and cut-off scores with a three-fold purpose: identification of aphasia, diagnosis of morphosyntactic and lexicosemantic impairments in aphasia. The outcomes of this project will improve diagnostic accuracy and therefore reduce health disparities for bilingual adults with aphasia.