This survey of patients discharged from 16 hospitals in Massachusetts sought to determine patients' perceptions of adverse events during hospitalization. Prior work in this area has demonstrated that patients can identify adverse events that were not documented in the medical record. One in four patients reported experiencing an adverse event during hospitalization, and most of these resulted in significant health consequences. A growing body of literature shows that patient surveys are an important method of detecting adverse events, and involving patients in safety efforts is a key component of providing patient-centered care.