It is accepted that kidney transplants that display delayed graft function (DGF) show poorer survival and function, particularly when an acute rejection episode (ARE) occurs. A diagnostic biopsy to establish the reason for DGF, or acknowledge an ARE, even if borderline, can improve short- and long-term graft survivals. From January 2002 to September 2006 we retrospectively evaluated 358 kidney transplant recipients. We performed a biopsy to evaluate the cause of DGF in all patients who required dialysis, or had serum creatinine levels that increased, remained unchanged, or decreased less than 10% per day on three consecutive days during the first week after transplantation. An ARE was found in 18.8% (n = 19) of the biopsies. Early biopsy for patients with DGF is a safe method that allows uncovering of an ARE that would otherwise be undetected. The immediate recognition and treatment of rejection episodes can certainly increase long-term survival and function of renal transplants.