The present invention relates to a device and a method for monitoring a patient access, particularly for monitoring the venous vascular access in extracorporeal blood treatment where blood is withdrawn from the patient via a flexible arterial line which has an arterial needle or cannula, and provided to the patient via a flexible venous line which has a venous needle or cannula. The needle or cannula of the present invention is so designed that, due to the liquid flowing through the needle or cannula, air is drawn in if the needle or cannula is out of the vascular access, whereby sound is generated. A vascular access which is not in proper order is detected with great certainty and reliability by monitoring the surrounding environment for the occurrence of sound, particularly for the occurrence of the solid-borne sound which propagates along the flexible venous line of the extracorporeal blood circuit.