National sharing of cadaveric renal allografts for perfectly matched kidneys (0 antigen mismatch) has improved outcome in the recipients of these kidneys despite increasing cold storage times. However, there may be limits to outcome improvement of matched kidneys based on age and cold storage time. To determine if national sharing of kidneys based on matching improves outcome regardless of donor age and cold storage time, we evaluated the United Network for Organ Sharing (UNOS) Scientific Registry for all recipients of cadaveric kidney transplants between January 1, 1990 and July 31, 1998. We divided the recipients into four groups based on donor age and cold storage time. Group 1 comprised young donors (donor age <55 years) with average (<24 h) cold storage time; group 2, young donors with long (>/=24 h) cold storage time; group 3, older donors (donor age >/=55 years) with average cold storage time; and group 4, older donors with long cold storage time. A total of 64,046 recipients were evaluated: 35,061 (55%) in group 1, 21,264 (33%) in group 2, 4308 (7%) in group 3, and 3414 (5%) in group 4. Early graft performance progressively decreased from group 1 to group 4. Delayed graft function (DGF: dialysis requirement in the first 7 days posttransplant) was 18, 29, 33, and 42% (P < 0.0001); serum creatinine at 3 years (in mg/dl) was 1.70 +/- 0.8, 1.73 +/- 0.9, 2. 31 +/- 1.0, and 2.42 +/- 1.1 (P < 0.0001); 1-year graft survival was 87, 84, 79, and 77% (P < 0.0001); and 3-year graft survival was 77, 74, 63, and 62% (P < 0.0001, for groups 1 and 2 vs groups 3 and 4, respectively). The trends in DGF persisted through the groups in 0 antigen mismatched kidneys. Early function is adversely affected by prolonged cold storage, despite matching, in recipients of younger and older donor kidneys. Long-term function does not appear to be affected by prolonged cold storage. Recipients of kidneys from donors >/=55 years of age have significantly worse short- and long-term outcome and may not benefit from national sharing. Copyright 2000 Academic Press.