The influence of donor age on the outcome of kidney transplantation (TX) was evaluated in 169 patients who received a primary cadaver kidney transplant at our center between September 16,1984, and December 31,1990. All the patients received cyclosporin A as part of the immunosuppressive protocol. Patients were grouped according to donor age: low donor age (LDA; donor age range 12-25 years), medium donor age (MDA; range 26-50 years) and high donor age (HDA; range 51-66 years). There were no differences between groups in graft and patient survival, and multivariate analysis did not show any effect of donor age on those parameters. Proteinuria/day and number of rejection episodes did not differ between groups either. Immediate diuresis was more frequent in group LDA than in the other two groups (73.8, 54.7 and 57.1%, respectively; p < 0.05) and immediate diuresis resulted as a weak positive prognostic factor for graft outcome at multivariate analysis (p = 0.05). At both univariate and multivariate analyses, donor age resulted inversely correlated with creatinine clearance (C<sub>Cr</sub>) at every period after TX but the 5th year, with r<sup>2</sup> from 0.12 to 0.23 (p < 0.01). The LDA group had significantly better C<sub>Cr</sub>than the HDA group at every period after TX but for the 5th year (the MDA group behaved intermediately). Moreover, in the 65 patients with a follow-up of 4 years or more, not only did the LDA group have the best C<sub>Cr</sub> (LDA vs. MDA and HDA: p < 0.02) but also C<sub>Cr</sub> remained roughly stable with time in groups LDA and MDA while it declined progressively with time in group HDA. The influence of donor age on hypertension after TX was negligible when compared to that of dialytic age and recipient sex. Our data show that kidneys from donors 12-25 years old give the best functional results, while those from donors over 50 are associated with the lowest kidney function. Moreover, if the reduced frequency of immediate diuresis and the progressive decline of C<sub>Cr</sub> with time are taken into account, kidneys from donors over 50 are also probably associated with reduced graft survival in the long term (after the 10th year). We suggest that kidneys from donors over 50 may be used, but they should be probably given to patients with a life expectation of no more than 10-15 years.