In problem-based learning (PBL), the role of a tutor or facilitator is different from what is typically considered as the role of a traditional teacher. In addition to being a subject-matter expert, the facilitator is also expected to be "socially" and "cognitively congruent". In this study, we analyze the survey responses from more than 10,000 students in order to better understand their perceptions of what makes a good or poor facilitator, and to identify specific qualities related to social congruence, cognitive congruence and use of expertise. Students' comments for the highest and lowest scoring groups of facilitators were analyzed qualitatively using inductive data analysis strategies. The following themes were identified: for social congruence--facilitator personality, relating to students, professionalism, motivating students, and learning environment; for cognitive congruence--scaffolding learning, and communication skills; for use of expertise--content knowledge and experience, and stretching students' learning. Coding of students' feedback also demonstrated that students most frequently commented on issues related to facilitators' social congruence. Our findings indicate that social congruence encompasses skills which facilitators may improve on. We also argue that understanding students' perspectives is critical especially in a learner-centred approach such as PBL and therefore propose that our findings provide useful input for the professional development of PBL facilitators.