Traditional methods of error detection have relied mainly on provider input or administrative data, without emphasizing the role of the patient in safety. This study of more than 2000 patients recently discharged from Massachusetts hospitals found that patients could identify unique adverse effects of hospitalization that may not have been identified by other methods. Importantly, physician reviewers agreed that the patient-reported events constituted a true clinical adverse event in more than 70% of cases. This finding corroborates prior research showing that patient-reported adverse events provide an important complementary perspective in assessing organizational safety problems.