This paper investigates the consequences of L2 use in university lectures. Data in the study stem from parallel lectures held by the same experienced lecturer in Danish (L1) and English (L2). It is found that the lecturer takes 22% longer to present the same content in L2 compared to L1, and that the lecturer speaks 23% more slowly in L2 than in L1. In the second part of the paper these differences are investigated through a qualitative analysis of parallel extracts from the same data set. Here it is found that when teaching in English the lecturer uses a higher degree of repetition and adopts a more formal and condensed style as compared to the rhetorical style in L1. Finally, the potential consequences of these quantitative and qualitative differences for student learning are discussed.