STUDY OBJECTIVE: To assess the usefulness of preoperative respiratory muscle training to increase muscle strength and its effects on postoperative pulmonary complications. DESIGN: We measured maximum inspiratory (MIP) and maximum expiratory (MEP) mouth pressure before and after training in 50 patients undergoing thoracic surgery. For control purposes, MIP and MEP were measured in 50 age- and sex-matched healthy subjects at two different times without training. RESULTS: Preoperative respiratory muscle training increased both MIP and MEP significantly (p < 0.01), while the control subjects showed no increase in these parameters. Eight patients who had postoperative pulmonary complications had significantly lower values (p < 0.01) and did not show significant increases in either MIP or MEP even after the training, unlike the other patients, who were without postoperative pulmonary complications. On the other hand, there were also another six patients who had equally low MIP and MEPs before training, but who raised their values with training and avoided the postoperative pulmonary complications. CONCLUSION: Preoperative respiratory muscle training may prevent postoperative pulmonary complications by increasing both inspiratory and expiratory muscle strength in patients undergoing thoracic surgery. Patients with respiratory muscle weakness have a higher risk of postoperative pulmonary complications.