The required result of correctly implemented endovascular treatment is bridging and elimination of the aneurysmatic sac from the blood flow in the aorta. Perfusion of the sac after release of the endovascular prosthesis is one of the most frequent complications of endovascular treatment. The majority of these perfusions is caused by a leak of the endovascular prosthesis at the site of the stented anastomosis, or more rarely by a collateral flow into the aneurysmatic sac or rupture of the endoprosthesis. Perfusion of the sac "endoleak" complicates endovascular treatment in cca 30%. During the postoperative period about half the perfusions recede spontaneously and about half require further treatment. Based on their own experience the author submits suggestions for the classification of leakage of endovascular prostheses with regard to the method of their treatment.