BACKGROUND: Thus far, incident reporting in health care has relied on health professionals. However, patients too may be able to signal the occurrence of undesirable events.OBJECTIVE: To estimate the frequency of undesirable events reported by recently discharged patients, and to identify correlates of undesirable events.DESIGN: Mailed patient survey.SETTING: Swiss public teaching hospital.PARTICIPANTS: Adult patients (N=1,518) discharged from hospital.MEASUREMENTS: Self-reports of 27 undesirable events during hospitalization, including 9 medical complications, 9 interpersonal problems, and 9 incidents related to the health care process.RESULTS: Most survey respondents (1,433, 94.4%) completed the section about undesirable events, and 725 (50.6%) reported at least 1 event. The most frequent events were phlebitis (11.0%), unavailable medical record (9.5%), failure to respect confidentiality (8.4%), and hospital-acquired infection (8.2%). The odds of an unfavorable rating increased with each additional interpersonal problem (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.3 to 1.8), each additional process-related problem (OR 1.5, 95% CI 1.3 to 1.9), but not with each additional medical complication (OR 1.0, 95% CI 0.9 to 1.2). Longer duration of stay, poor health, and depressed mood were all related to a greater reported frequency of undesirable events.CONCLUSION: Patients are able to report undesirable events that occur during hospital care. Such events occur in about a half of the hospitalizations, and have a negative impact on satisfaction with care.