Patient safety is an important issue in medical quality control. To our knowledge, no studies have been conducted to specifically address patient safety in surgery in Taiwan. The purposes of this study were to determine the incidence of surgical errors in Taiwan, to evaluate the effectiveness of a campaign to mark the planned operation site, and the factors that influence the frequency of this preoperative safety maneuver. Methods: In March 2004, each member of the Taiwan Orthopaedic Association was given a 12-question survey regarding wrong-site, wrong-patient, and wrong-procedure errors to provide baseline data. We then implemented a campaign to encourage orthopedic surgeons to mark the planned operation site („Mark op site” campaign). A follow-up survey was done in October 2004, and the results of both surveys were compared. Results: On the second survey, the number of surgeons who marked the incision site had significantly increased (p < 0.05), and the incidences of reported wrong-site (0.5%) and wrong-procedure errors (2.4%) were lower than on the first survey (4.8%, p < 0.05 and 5.6%, p < 0.05). On the second survey, preoperative marking of the incision site was significantly correlated with the location of the surgeon's practice. Conclusion: Orthopedic surgeons marked the incision sites more frequently after our campaign than before, suggesting that the campaign was effective in changing their behavior. In Taiwan, this campaign reduced the risk of wrong-site and wrong-procedure errors. [J Formos Med Assoc 2007;106(3):212-216]