Tests of knowledge, aptitude and psychomotor skills have been used to assess and select surgical trainees but none of these is reliable in the long term. The industrial quality-control method of the cusum was used to assess performance progress in 17 surgical trainees. Trainees were assessed on their ability to perform, independently, selected surgical operations using the criterion of procedure duration. Cusum profiles were compared with scores from at least four independent assessors using a modified Royal Australasian College of Surgeons' mentor form. The cusum identified all trainees who were considered either satisfactory or less able by their mentors. This objective evaluation was reliable after 25 procedures, whether for appendicectomy or combined with herniorrhaphy and cholecystectomy. Evaluation of surgical performance using the cusum may prove to be a more objective tool for assessing surgical trainees than early impressions or less clinically oriented tests.