We sought to determine whether patients or their families could identify adverse events in the emergency department (ED), to characterize patient reports of errors and to compare patient reports to events recorded by health care providers. This was a prospective cohort study in a quaternary care inner city teaching hospital with approximately 40,000 annual visits. ED patients were recruited for participation in a standardized interview within 24 hours of ED discharge and a follow-up interview 3-7 days after discharge. Responses regarding events were tabulated and compared with physician and nurse notations in the medical record and hospital event reporting system. Of 292 eligible patients, 201 (69%) were interviewed within 24 hours of ED discharge, and 143 (71% of interviewees) underwent a follow-up interview 3-7 days after discharge. Interviewees did not differ from the base ED population in terms of age, sex or language. Analysis of patient interviews identified 10 adverse events (5% incident rate; 95% confidence interval [CI] 2.41%-8.96%), 8 near misses (4% incident rate; 95% CI 1.73%-7.69%) and no medical errors. Of the 10 adverse events, 6 (60%) were characterized as preventable (2 raters; kappa=0.78, standard error [SE] 0.20; 95% CI 0.39-1.00; p=0.01). Adverse events were primarily related to delayed or inadequate analgesia. Only 4 out of 8 (50%) near misses were intercepted by hospital personnel. The secondary interview elicited 2 out of 10 adverse events and 3 out of 8 near misses that had not been identified in the primary interview. No designation (0 out of 10) of an adverse event was recorded in the ED medical record or in the confidential hospital event reporting system. ED patients can identify adverse events affecting their care. Moreover, many of these events are not recorded in the medical record. Engaging patients and their family members in identification of errors may enhance patient safety.