Introduction: This study examined the validity of tensiometry as an objective method of assessing the improvements in the quality of knots and technical performance due to practice on suturing and knot-tying skills. Methods: We evaluated the quality of 1,830 knots produced by undergraduate medical students before training (pre-test), after (post-test), and after a week retention (retention-test) using tensiometry. These results were compared to expert-based assessments of products and performance. Results: Tensiometry, as well as expert-based assessments can detect changes in the quality of knots and technical performance from pre- to post- and retention-test (p less than 0.05). However, these three methods may assess different dimensions of the same products and actions. Conclusions: The development of trainee evaluation criteria for the acquisition of surgical skills is a crucial element in surgical education. Based on our patterns of results it is hypothesized that tensiometry can serve as an economic first approximation of the quality of knots and suturing performance.