Transplant renal artery stenosis (TRAS) is a recognized, potentially curable cause of posttransplant arterial hypertension, allograft dysfunction, and graft loss. It usually occurs 3 mo to 2 yr after transplantation, but early or later presentations are not uncommon. The prevalence ranges widely from 1 to 23% in different series, reflecting the heterogeneous criteria used to establish the diagnosis, the different manner of preservation of the graft, and surgical expertise. Reported cases are progressively increasing in parallel with the use of non-invasive investigation procedures, such as Doppler ultrasonography and magnetic resonance (MR) angiography, that arouse the suspicion of the disease even in less symptomatic cases. However, definitive diagnosis of hemodynamically significant stenosis rests on the use of invasive angiographic techniques. Percutaneous transluminal angioplasty (PTA) is the treatment of choice and restores kidney perfusion in 60 to 90% of cases. The risk of re-stenosis, the major drawback of the procedure, is prevented by the use of expandable endoprostheses. Surgery is indicated for stenoses that cannot be treated by PTA or that recur after it. Doppler ultrasonography is the procedure of choice to evaluate graft perfusion before and after revascularization.