Introduction: For health professionals, the development of insight into their performance is vital for safe practice, professional development and self-regulation. This study investigates whether the development of dental trainees' insight, when provided with external feedback on performance, can be assessed using a single criterion on a simple global ratings form such as the Longitudinal Evaluation of Performance or Mini Clinical Evaluation Exercise. Methods: Postgraduate dental trainees (N = 139) were assessed using this tool on a weekly basis for 6 months. Regression analysis of the data was carried out using SPSS, and a short trainer questionnaire was implemented to investigate feasibility. Results: Ratings for insight were shown to increase with time in a similar manner to the growth observed in other essential skills. The gradient of the slope for growth of insight was slightly less than that of the other observed skills. Trainers were mostly positive about the new criterion assessing trainees' insight, although the importance of training for trainers in this process was highlighted. Discussion: Our data suggest that practitioners' insight into their performance can be developed with experience and regular feedback. However, this is most likely a complex skill dependent on a number of intrinsic and external factors. Conclusion: The development of trainees' insight into their performance can be assessed using a single criterion on a simple global ratings form. The process involves no additional burden on evaluators in terms of their time or cost, and promotes best practice in the provision of feedback for trainees.