An IOM report highlights diagnostic errors as common patient-safety problems. Its recommendations address myriad system features and activities affecting diagnosis, acknowledging that many contributing factors are intricately related to health care delivery problems. The 1999 Institute of Medicine (IOM) report To Err Is Human transformed thinking about patient safety in U.S. health care. On its 15th anniversary, a topic largely missing from that report is finally getting its due. With its new report, Improving Diagnosis in Health Care, the IOM has acknowledged the need to address diagnostic error as a “moral, professional, and public health imperative.” 1 The new report emphasizes that diagnostic errors may be one of the most common and harmful of patient-safety problems. Why has it taken so long for the patient-safety movement to recognize the importance of diagnostic errors? Perhaps . . .