In the third year of medical school students are exposed to many stressful and potentially traumatic events, including witnessing patient suffering or death, personal mistreatment, and poor role modeling by physicians. These experiences may explain increases in anxiety and depression during medical school. However, to date this has not been studied. The present study prospectively measured stressful clerkship events occurring during the 2006-2007 academic year in third-year medical students of the Mount Sinai School of Medicine (n = 125), using surveys completed monthly. Students labeled stressful events traumatic if they met the trauma criteria of the Diagnostic and Statistical Manual of Mental Disorders, fourth edition. The authors measured anxiety, depression, and posttraumatic stress symptoms at the beginning and end of the year and twice during the year. At year's end they also measured students' personal growth. Class participation varied from 106 (85%) at baseline to 82 (66%) at endpoint. Most students (101; 81%) completed at least one monthly survey. Many students reported exposure to trauma as well as personal mistreatment and poor role modeling by superiors. Trauma exposure was positively associated with personal growth at year's end. In contrast, exposure to other stressful events was positively associated with endpoint levels of depression and other stress symptoms. Trauma exposure was common but not associated with poor outcomes by year's end, which suggests that students were resilient. Nonetheless, unprofessional behavior by resident and attending physicians might have adverse effects on the well-being of students.