Restenosis literally means the reoccurrence of stenosis (an abnormal narrowing in a blood vessel or other tubular organ or structure). This is usually restenosis of an artery, or other blood vessel, but possibly any hollow organ that has been "unblocked". This term is common in vascular surgery, cardiac surgery or interventional cardiology following angioplasty, all branches of medicine that frequently treat stenotic lesions.

There are probably several mechanisms that lead to restenosis. An important one is the inflammatory response, which induces tissue proliferation around an angioplasty site.

Cardiologist have tried a number of approaches to decrease the risk of restenosis. Stenting is becoming more commonplace; after balloon angioplasty, a metal mesh is pressed against the wall of the artery that has been opened, decreasing the risk of restenosis. Other approaches include local radiotherapy and the use of immunosuppressive drugs, coated onto the stenting mesh. Analogues of rapamycin, such as tacrolimus (FK-506), sirolimus and more so everolimus, normally used as immunosuppressants but recently discovered to also inhibit the proliferation of vascular smooth muscle cells, have appeared to be quite effective in preventing restenosis in clinical trials.