Anxiety has been identified as a plausible factor affecting second language (L2) acquisition. However, more research is needed on how anxiety may influence Spanish-speaking adult English as a Second Language (ESL) populations. Determining precisely what causes anxiety in Spanish-speaking adult ESL populations should be of interest not only to L2 researchers but also to ESL instructors who may have adult Spanish-speaking English language learners (ELLs) in their classes. This study researched L2 anxiety in Spanish-speaking adult ESL learners. Specifically, it considered possible causes and cultural influences of L2 anxiety in 10 Spanish-speaking adult ESL students at a university English language institute (ELI). Participants were given a choice of completing an English or Spanish version of the Foreign Language Classroom Anxiety Scale (FLCAS) and then participated in follow-up interviews. Results were documented and evaluated. A total of 14 causes of L2 anxiety were identified, including incompatible goals, using English in professional contexts, the native country, and the need for error correction. Finally, contrary to the literature, collaborative group work was found to cause L2 anxiety in Spanish-speaking adult ESL students enrolled at a language institute.