BACKGROUND To investigate the effects of age and gender matching on patient and graft survival in living unrelated kidney transplantation. METHODS All 2649 first-time kidney transplanted cases who had received their graft from a living unrelated donor in Baqiyatallah Hospital (Tehran, Iran) were enrolled (1992-2005). Based on the age and gender matching state of the donors (D) and recipients (R), the recipients were divided into four age-match (A) and four gender-match (G) groups. Age-match groups included A(1) (R< or =40, D< or =40, n=1483), A(2) (R>40, D< or =40, n=1044), A(3) (R< or =40, D>40, n=82) and A(4) (R>40, D>40, n=40). Gender-match groups comprised G(1) (R: female, D: female, n=209), G(2) (R: male, D: male, n=1428), G(3) (R: female, D: male, n=768) and G(4) (R: male, D: female, n=244). Using Kaplan-Meier method, 6-month, to 5-year graft/patient survival rates were determined for different patient groups. Survival curves were compared using log rank test after stratification. RESULTS Male recipients living with a female donor's kidney had a shorter survival compared to both the males having received a male kidney and the females having received a female kidney. Graft survival also showed a marginally significant difference and was shorter among the males with a female kidney graft compared to the males living with a male kidney graft. In contrast, donor's sex caused no difference in patient or graft survival among female recipients. When survival curves of age-match groups were compared, both graft and patient survival times were significantly shorter among the younger patients having a kidney graft received from an older donor. Patient survival was also shorter among old recipients having received an old kidney compared with old patients having a kidney graft from a young donor. Though graft survival among the old patients with old grafts was also shorter than in those with young grafts, the difference was not significant. When the subjects were stratified by donors' age, the results showed that old patients with young kidneys survived shorter than young patients with young kidneys. CONCLUSIONS Better living unrelated renal transplantation outcome is expected with younger kidney grafts (i.e. donor < or =40 yr) and avoiding grafting female kidneys into male recipients.