Medical students need to be well informed about medical errors and patient safety. Pursuant to a needs assessment and pilot program, 229 third-year students participated in a 1-day program on patient safety including a plenary session and workshops. Attitudes and beliefs were measured by a survey at the beginning and end of the program. Completed surveys were returned by 124 (54%) students. Their level of agreement with 14 of 21 rating scale items changed in the expected direction. There were 7 items in which the students' baseline responses were already positive and did not change significantly. A 1-day program on patient safety in the third year of medical school can change students' attitudes and beliefs. There may be a subset of students needing closer attention. The findings provide evidence for the validity of the attitude survey and reinforce the effectiveness of interclerkship programs in medical schools.