PURPOSE: This study investigated the impact of subclinical borderline changes on the development of chronic allograft injury in patients using a modern immunosuppression protocol. METHODS: Seventy patients with stable renal allograft function and who underwent protocol biopsies at implantation, 10 days and 1 year after transplantation were included and classified based on biopsy findings at day 10. The no rejection (NR) group included 33 patients with no acute rejection. The treatment (Tx) group included 21 patients with borderline changes following steroid pulse therapy, and the nontreatment (NTx) group included 16 patients with borderline changes nontreated. RESULTS: The Banff Chronicity Score (BChS) and modified BChS (MBChS) were not different among the three groups at implantation (P = 0.48) or on day 10 (P = 0.96). Surprisingly, the NTx group had more prominent chronic scores at the 1-year biopsy, including BChS (3.07 +/- 1.33, P = 0.005) and MBChS (3.14 +/- 1.41, P = 0.008) than those in the Tx and NR group, and deterioration of BChS was more noticeable in the NTx group (P = 0.037), although renal function was stable (P = 0.66). No difference in chronic injury scores was observed between the Tx and NR groups at the 1-year biopsy. CONCLUSION: Subclinical borderline changes can be a risk factor for chronic allograft injury and should be considered for antirejection therapy.