In the quest to improve patient safety, diagnostic errors have been underemphasized and as a result have been termed the "next frontier" for the safety field. This systematic review of autopsy studies sought to estimate the incidence of diagnostic errors contributing to death (class I errors) in intensive care unit (ICU) patients, compared with a prior systematic review that identified a 4.1% class I error rate across all patients undergoing autopsy. This review, which included 31 separate studies, found an overall class I error rate of 8% in ICU patients, with vascular events and infections accounting for most missed diagnoses. Despite the continuing utility of autopsies in improving diagnostic performance, autopsy rates in the United States have been steadily declining, leading to calls for efforts to increase autopsy rates.