Background: Simulation-based training provides minimal feedback and relies heavily on self-assessment. Research has shown medical trainees are poor self-assessors. The purpose of this study was to examine trainees' ability to self-assess technical skills using a simulation-trainer. Methods: Twenty-one medical students performed 10 repetitions of a simulated task. After each repetition they estimated their time and errors made. These were compared with the simulator data. Results: Task time (P < 0.0001) and errors made (P < 0.0001) improved with repetition. Both self-assessment curves reflected their actual performance curves (P < 0.0001). Self-assessment of time did not improve in accuracy (P = 0.26) but error estimation did (P = 0.01) when compared with actual performance. Conclusions: Novices demonstrated improved skill acquisition using simulation. Their estimates of performance and accuracy of error estimation improved with repetition. Clearly, practice enhances technical skill self-assessment. These results support the notion of self-directed skills training and could have significant implications for residency training programs. © 2003 Excerpta Medica, Inc. All rights reserved.