Status 1 is the listing category reserved for patients awaiting liver transplantation who are at risk of imminent death. This high allocation priority was intended to benefit patients with acute liver failure and children with severe chronic liver failure. However, the status 1 criteria were not well defined. The aims of this study, which used the Organ Procurement and Transplantation Network/Scientific Registry of Transplant Recipients database for patients wait-listed between February 27, 2002, and September 30, 2003, were to determine the indication and numbers of children and adults at status 1 (including regional variations); examine death rates on the waiting list for children at vs. not at status 1; and examine time to death, transplant, or removal from the waiting list for both pediatric and adult status 1 candidates. During the study period, 40.3% of children and 6.1% of adults were transplanted at status 1. The indication was acute liver failure in 52.1% of adults and 31% of children. Among status 1 transplants, Regional Review Board exceptions were granted for 16.7% of children and 10.1% of adults. Death rates for children listed at status 1 by exception per patient-year at risk were substantially lower (0.51) than those of children with acute liver failure (4.06) or with chronic liver disease and Pediatric End-Stage Liver Disease score > or =25 (4.63). The percentage of adults who died while on the waiting list within 90 days of listing was more than twice that of children, whereas the percentages transplanted were similar. Patients listed and transplanted at status 1 were a heterogeneous population with an overrepresentation of children with varying degrees of chronic liver disease and other exceptions, and an associated wide variation in waiting list mortality. Recent changes in status 1 criteria provide stricter definitions, particularly for children, including the removal of the "by exception" category, with the intent that all candidates listed at status 1 share a similar mortality risk.