The patient safety consequences of diagnostic errors have been receiving greater attention in the past few years, after being relatively neglected in the early period of the safety movement. The results of this study will likely add momentum to this "next frontier" in patient safety. The authors analyzed 25 years of closed malpractice claims from the National Practitioner Data Bank and found that diagnostic errors—primarily in the outpatient setting—were both the most common and the most costly (in terms of total payments) type of claim. Compared with other types of errors, diagnostic errors were more likely to result in serious patient harm or death. Although data from closed malpractice claims may not be representative of all error types, it is clear from this study that diagnostic errors account for a large proportion of preventable patient harm. Recent reviews have identified strategies to improve diagnostic accuracy at the individual clinician level and at the system level. The human costs of a fatal diagnostic error—for the patient and the clinician—were vividly illustrated in a recent graphic-novel style article.