This article discusses the notion of ‘language barrier’ regarding communication with patients with a migration background. These patients usually show some level of proficiency in the official language of the hospital. However, their proficiency is usually limited so that they still need interpreters to communicate effectively with medical staff. Thus, the language constellation between participants is partly “transparent”, to use Müller’s (1989) term. Based on two case studies it will be shown that the forms of participation of interpreters in such interactions are influenced by the specific multilingual competencies of the patients.