Restenosis after percutaneous transluminal coronary angioplasty is a critical factor limiting the usefulness of this procedure. It has been reported to occur in 25% to 50% of patients averaging 33%. In the majority of patients it appears within 6 months after procedure. Some clinical, angiographic and procedural factors can predict higher incidence of restenosis--they are discussed in the article. Main mechanisms which result in restenosis are intimal hyperplasia and smooth muscle cellular proliferation. Exercise thallium-201 scintigraphy and coronary angiography are the best methods in diagnosis of restenosis. The prevention and the therapy of restenosis appear as a difficult problems. Successful pharmacological approach doesn't exist until now. In about 50% of patients with restenosis coronary angioplasty is repeated with the same success and restenosis rate as in the first angioplasty.