To explore student perceptions of factors contributing to the effectiveness of discussions in the reporting phase of the problem-based learning (PBL) process, where students report and synthesise the results of self-study. Forty-eight Year 1 and 2 medical students participated in 6 focus group interviews about the characteristics of effective group discussions and possible improvements. The data were analysed qualitatively in several stages. The analysis yielded 4 main characteristics of effective discussions: asking for, giving and receiving explanations; integrating and applying knowledge; discussing differences with regard to learning content, and guiding and monitoring the content and the group process of the discussion. Integrating and applying knowledge included structuring, relating and summarising information and providing examples from practice. Discussing different opinions included discussing a variety of literature resources and disagreements. The main learning effects mentioned by the students were retention, understanding, integration and application of knowledge. Students have clear ideas about what promotes effective discussions during the reporting phase. Their PBL experience has provided them with some insights that are in line with theory and research on collaborative learning. Future research should examine differences between student and tutor perceptions of the quality of discussions. Introductions to PBL for students and tutors should include training in asking open but focused questions, supporting explanations with arguments and dealing with conflicts about learning content. Tutors should be trained in giving effective and personal feedback. Collaborative creation of external knowledge representations (i.e. concept maps) should be advocated, as should variety of literature resources.