The aim of this study was to determine the incidence and possible causes of delayed graft function (DGF) and its impact on outcome in living-related kidney transplantations. We analyzed 158 consecutive living-related kidney transplant recipients. DGF is described as the failure of serum creatinine to fall below pretransplant levels within 1 week of the operation, regardless of urine output. Of the 158 patients studied, 14 (8.8%) fit this criterion. Donor and recipient factors such as age, gender, body weight, recipient/donor weight ratio, HLA match, cyclosporine level, blood group, and anastomosis time of patients with DGF were compared to those of patients without DGF. Apart from donor gender, body weight, and recipient/donor body weight ratio, these parameters were similar in the two groups. In the DGF group the majority of the donors were female (11/14), whereas this was not the case in the controls (64/144; p < 0.02). Mean donor weight in patients experiencing DGF (59.6 +/- 9.2 kg) was significantly lower than in those without DGF (67.8 +/- 10.4 kg; p < 0.05). The mean recipient/donor weight ratio for the DGF group (1.26) was significantly higher than that of the control group (1.03, p < 0.02). The 5-year graft survival rates for patients with and without DGF were 74% and 77%, respectively (NS). On the other hand, the 5-year graft survival rate for patients with DGF complicated by an acute rejection episode (n = 6, 61%) was significantly lower than that of control group patients who experienced acute rejection (n = 43, 74%; p < 0.02). These results indicate that female donor gender and higher recipient/donor weight ratio are major predictive factors in the development of DGF following living-related kidney transplantation. Although DGF alone did not affect the outcome, long-term graft survival was significantly reduced when DGF was associated with acute rejection episodes.