English medium education at university level is widely used in different contexts and it poses a challenge for students who are not used to studying through the medium of English. This study was carried out in a university in the Basque Country in Spain and it focuses on a course where students who are mostly Basque-Spanish bilinguals are taught through the medium of English. The course teacher applies a flexible language policy allowing for the use of three languages in the class. The aim of this study is to analyse the languages used by the teacher and the students and the students' reactions towards the use of three languages. The instruments used were a background questionnaire, classroom observations, focus group discussions and students' journals. The results indicate that there are important differences between the language used by the teacher and the students and also that most students responded positively to the flexible language use.