Diagnostic error has recently garnered attention as a patient safety problem, as evidenced by the publication of a major report on the topic by the Institute of Medicine. This commentary describes why diagnostic errors previously received less attention than other safety efforts and highlights the importance of addressing this issue. The authors emphasize that diagnostic errors have become even more important in light of the growing clinical and financial costs of these errors in health care. They recommend strategies to improve diagnosis, such as establishing a formal curricula for educating trainees about misdiagnosis and developing validated metrics to determine how frequently diagnostic errors occur and understand their downstream health and economic implications.