This paper discusses quality assessment of the performance of both professional and student interpreters working in various contexts, using a wide range of methods. It then focuses on self-evaluation by trainee simultaneous interpreters as examined in two empirical studies. The first project applied retrospective verbal protocols to investigate interpreting strategies used by 36 advanced student interpreters working in both directions between Polish (A) and English (B). The results concerning self-evaluation, which are presented here, were a by-product of this first study, but they gave rise to questions that are further explored in the second project. Eighteen subjects at the same stage of training were asked to interpret a text from English into Polish and to evaluate their performance, linking it to the strategic processing they had applied. The results suggest a significant trend towards negative assessment, combined with most attention being devoted to faithfulness to the original message and to completeness. Issues of presentation (including monotonous intonation, hesitant voice and long pauses), on the other hand, were hardly ever mentioned.