OBJECTIVE To study the effects of a patient safety and medical fallibility curriculum on second-year medical students at the University of Missouri-Columbia School of Medicine in 2003-2004. METHODS Students completed a knowledge, skills, and attitudes questionnaire before the curriculum, after the final learning experience, and one year later. A 95% confidence interval (CI) for paired differences assessed change over time. At one year, students also responded to items about their use of the curriculum, error reporting, and disclosure experiences. RESULTS Fifty three of 92 students (55%) completed the questionnaire at all three assessment points. Students' eight items and the calculated knowledge score improved after the curriculum but only seven of these improvements were sustained one year. Responses to seven items did not change and five changed in an undesired direction after the curriculum and/or after one year. Seventy two students completed the self-reported behavior questions at one year. More than half reported using what they learned in the curriculum. Although 76% of students reported observing an error, 71% of these disclosed an error to their peers, 56% to a resident, and 46% to faculty. Only 7% reported an error using our electronic error reporting system. CONCLUSIONS The curriculum led to changes in second-year medical students' knowledge, skills, and attitudes, but not all of the changes were sustained at one year, were in the desired direction, or were supported by their self-reported behaviors. The extent to which other informal or hidden curriculum experiences reversed the gains and affected the changes at one year is unknown.