The study aims to analyze the factors affecting performance of tutors during problem-based learning (PBL) implementations. This study employs a case study design in order to identify and analyze PBL implementations providing detailed and rich descriptions through the perceptions of tutors and students. To this end, four tutors and fourteen students were selected for the case study. The data utilized in this study were collected by means of observations and interviews. The findings of this study indicated that tutors' level of adaptation of the PBL and their content expertise were commonly mentioned as factors affecting their performance during PBL implementations. (C) 2010 Elsevier Ltd. All rights reserved.