A method and a device for monitoring an extracorporeal blood flow during an extracorporeal blood treatment with an extracorporeal blood treatment device. The extracorporeal blood treatment device may include the device for monitoring an extracorporeal blood flow. The arterial and/or venous patient access is monitored with a first and a second method, each of which there is a check for a presence of at least one criterion that is characteristic of a condition of the vascular access that is not in proper order, the criteria for the first and second methods being distinguished from one another. A blood pump, which is preferably an occlusion blood pump, is stopped once the presence of the at least one criterion of the first method has been established, while a venous cut-off unit remains open. Once the blood pump has been stopped, the presence of the at least one criterion is checked with the second method. The venous cut-off unit is not closed until the at least one criterion for the second method is present. Otherwise the blood pump is restarted to continue the blood treatment.
