As shown in studies using angioscopy, thrombus formation over the DES struts can be seen as long as 6 months after PCI. The effect is probably caused by the inhibitory effects of immunosuppressive, antimitotic and antiinflammatory drug released from the stent on the EPCs adhering to the place of vascular injury and the struts. The use of DES significantly reduced the risk of ISR, but the slowing and prolongation of the reparatory process may increase the risk of the late in-stent thrombosis as well as other unwanted effects, such as edge effect and formation of the coronary aneurysms. The risk of late thrombotic effects of DES is mainly associated with discontinuation of dual antiplatelet therapy, therefore the treatment should be continued for at least 12 months or even indefinitely. The following groups of patients have a particularly high risk of in-stent thrombosis: acute coronary syndromes, cardiogenic shock, diabetes, procedure-related parameters (coronary dissection, long lesion, small vessel diameter, use of multiple stents). On the other hand, prolonged dual anti-platelet therapy is associated with significant risk (bleeding, thrombocytopenia) especially in patients with peptic ulcer disease and in the elderly. Discontinuation of this therapy is also indicated in patients undergoing surgery, which may increase the risk of thrombotic events.