In Swedish language planning the position of English vis-à-vis Swedish is attracting attention. This is due to the concern that the growing use of English in certain domains may result in Swedish loosing ground. Surveys have shown that English is frequently used in fields with extensive international collaboration, such as higher education, business and politics. Yet, knowledge about actual language use and patterns of language choice in international contexts is poor and studies on how the involved parties themselves understand the situation are lacking. This paper draws on data from an ongoing PhD project on the use of Swedish in English medium university education and discusses students’ language choice patterns in two English medium lectures in Sweden: the one taken from a faculty of social sciences and the other from a faculty of science and technology. Findings show that the use of Swedish differs between the two lectures and that the usage can be characterized as spontaneous. Interestingly, students speak Swedish in a number of study activities associated with the lectures. Even though Swedish is seldom heard in class, it dominates in study activities outside class. The number of exchange students in combination with students’ and teachers’ attitudes impact on language choices. Existing local language plans, however, do not seem to influence actual language use.