The critical shortage of organs available for renal transplantation has led to the consideration of alternative strategies for increasing the donor pool. Recently, the cadaveric kidney donor pool extended to donors who might have been deemed unsuitable in early times, leading to the concept of marginal donors and more recently to the notion of expanded criteria donors. Such organs are eligible for organ donation but, because of extreme age and other clinical characteristics, are expected to produce allograft at risk for diminished post-transplant function. Thus, the challenge is now to reduce the difference between graft outcome from patients grafted with marginal and 'optimal' donors. This implies appropriate transplantation strategies during pre-, peri- and post-transplantation phases including reduction of cold ischemia time, recipient selection, adaptation of immunosuppressive drug regimens, increase in nephron mass by dual kidney transplantation, and improvement in the graft selection process using histological criteria. This review summarizes current definition of a marginal donor and provides some guidance for clinical management of such transplant.