To evaluate the educational effects of a lung-sound auscultation simulator, “Mr. Lung”, we compared outcomes of fifth-year medical students in 2001 and 2002. From June 2001 through March 2002, we used “Mr. Lung” for small-group teaching for 100 fifth-year medical students. The following year, we opened our laboratory so that the fifth-year students could study with “Mr. Lung” by themselves for 1 month. “Mr. Lung” was then used for objective structured clinical examinations in May 2002. From June 2002 through April 2003, we used “Mr. Lung” again for small-group teaching for 91 fifth-year students. The class consisted of 90 minutes' training for the auscultation of lung sounds. At the beginning of class, auscultation tests were performed in which the students listened through their stethoscopes to 3 examples of abnormal lung sounds on “Mr. Lung” and answered questions about the location and quality of the sounds. The percentages of correct answers in 2001 and 2002, respectively, were 36.9% and 35.4% for differences between bilateral lung sounds, 52.5% and 55.8% for coarse crackles, 34.1% and 58.3%(p<0.05) for fine crackles, 69.2% and 70.8% for wheezes, 62.1% and 90.7%(p<0.01) for rhonchi, and 22.2% and 32.6% for stridor. In conclusion, 1 month's self-study with “Mr. Lung” to prepare for the objective structured clinical examinations improves auscultation skills.