Translanguaging has become a very relevant and controversial issue, especially in those contexts where the language teaching tradition encourages the exclusion of the L1 from the L2/FL classroom. Whereas previous research in the Basque Country has mainly focused on the implementation of translanguaging pedagogies, in this study we carried out a contrastive analysis of translanguaging practices in English Medium Instruction (EMI) and Basque Medium Instruction (BMI) at the University of the Basque Country. We observed and videotaped 29 lessons (39 hours) of two teachers who taught their subjects both in an EMI group and a BMI group. We also gathered students' and teachers' beliefs and attitudes towards translanguaging. 455 students completed a questionnaire and interviews were conducted with both teachers. The tool used for the observation and analysis of the recorded lessons was based on the COLT [Spada, N., & Fröhlich, M. (1995). "COLT--communicative orientation of language teaching observation scheme: Coding conventions and applications." National Centre for English Language Teaching and Research] observation scheme. The results showed some significant differences when we compared translanguaging in EMI and BMI. However, the teacher variable turned out to be more influential than the language of instruction. Moreover, both teachers and students showed more negative than positive attitudes regarding translanguaging practices.