We have reviewed the outcome of kidney transplantations where both kidneys retrieved from the same donor were transplanted at our Department and the factors which might be decisive in the outcome. Between 1973 and 1996, 1325 kidney transplantations were performed at our Department. In 360 cases, both kidneys retrieved from the same donor were transplanted at our Department. We evaluated only first transplant cases who were treated with a combination of cyclosporin and prednisolon. After this selection, 248 pairs of kidneys were left for analysis. We divided them into three groups. The first comprised immediately functioning kidneys (135 pairs), the second, no immediate graft function in any of the recipients (29 pairs). The third group was mixed: the kidneys retrieved from the same donor were functioning in one recipient and not in the other, so this group was omitted from the analysis. We therefore analysed the donor factors of age, sex and cause of death. We found no significant difference between the groups relating to the cause of donor death. There was, however a significant difference in the age of donors: those kidneys functioning well in both recipients derived from a younger donor group (16-40 years), 18/58 versus 136/270, P < 0.01, chi 2 = 7.17. There were significantly fewer older donors (41-65 years) in the immediately functioning group than in the other, 38/58 versus 110/ 270, P < 0.001, chi 2 = 11.84. We investigated the number of HLA mismatches, ischaemic time, cytotoxicity index and the type and duration of pretransplantation dialysis. It appears from this analysis that the age of the donor is a significant factor in the short-term outcome of transplanted kidneys. Recipient factors as HLA match, ischaemic time and cytotoxicity index seems to be less important.