Language learning strategies (LLS) are suggested to facilitate learning and support learner autonomy. The integration of content and language in foreign language education increases the cognitive work load. Furthermore, self-efficacy has been identified as a key predictor for strategy use and language achievement. The present study aimed to (1) investigate LLS use in content-based versus traditional foreign language environments and (2) assess the impact LLS use and self-efficacy have on language proficiency. Participants were Year 9 Content and Language Integrated Learning (CLIL) and regular English as a foreign language (EFL) students (N=378) in Germany. Structural equation modelling, controlling for a range of confounding variables, showed that (1) there was no difference in LLS use between CLIL and EFL students. (2) LLS use had a negative impact while self-efficacy predicted higher language proficiency. These results suggest that students may best be supported by enhancing their self-efficacy while they should carefully choose their strategies.