Self-assessment is argued to be valuable educationally and is being advocated through policies for wider adoption within medical practice. However, students are often reluctant to self-assess and little research has examined the reasons for this. This study explored the perceptions of trainees and postgraduates on assessment and self-assessment of surgical skills. Data were collected through semi-structured interviews conducted with six trainees and postgraduate students in Oral Surgery. They had previously been assessed, and self-assessed themselves for the first time, while surgically removing a mandibular third molar tooth. Assessments were judged against both an objective checklist scale and a global rating scale. Eight themes were identified and trainees' comments on these themes analysed. The themes identified were assessment and stress, pressure to over- or under-score, the impact of self-assessment on learning, reflection and performance, confidence and the necessity of preparation, acceptability of the scales and criteria used, feedback, and the acceptability of self-assessment. In conclusion we need to instill in our trainees a culture whereby they feel capable of and comfortable making judgements about their own performance and giving and receiving constructive assessment from their peers.