The objectives of this study were to examine if pre-stroke proficiency predicts post-stroke lexical semantic performance in Spanish-English bilingual persons with aphasia (PWA) and identify patterns of impairment in this population. A language use questionnaire was administered to 27 Spanish-English bilingual PWA to measure pre-stroke proficiency in both languages. Standardized language assessments in Spanish and English were administered to measure post-stroke lexical semantic performance in both languages. A principal component analysis was conducted on the language use questionnaire measures, revealing Daily Usage, Education, Exposure, and Language Ability Rating as factors that contribute to a person’s proficiency in their first language (L1), and Age of Acquisition, Daily Usage, Family Proficiency, Education, Exposure, Confidence and Language Ability Rating as factors that contribute to a person’s proficiency in their second language (L2). Regression analyses revealed that pre-stroke proficiency significantly predicted post-stroke lexical semantic performance, most strongly in English than in Spanish. Two distinct patterns of impairment emerged within the participants: parallel impairment and differential impairment. Overall, these results confirm that pre-stroke language proficiency is a key determiner of performance on standardized language assessments post-stroke, such that the higher proficiency pre-stroke, the higher performance on standardized tests post stroke. This pattern was more clear when English was L1 or L2 relative to when Spanish was L1 or L2. These results have important implications for assessment and diagnosis of aphasia in bilingual individuals particularly when clinicians need to select the language of assessment.