The natural history of coronary aneurysms, defined as local dilatations exceeding the diameter of the normal adjacent vessel segments by at least 1.5 times, is not significantly different from the natural history of nonaneurysmal coronary disease. However, little is known about the prognosis of percutaneous transluminal coronary angioplasty (PCTA)-induced coronary aneurysms. Therefore, we investigated the occurrence and the medium long-term prognosis of such aneurysms in 728 patients who, after successful PTCA, underwent repeat coronary angiography at mean 4.5 months post-PTCA. A coronary aneurysm at the site of PTCA ws noted in 3.9% of patients (n = 28). Of the potentially predictive factors analyzed, only a coronary dissection at the time of PTCA had statistically significant influence. The long-term prognosis of PTCA-induced coronary aneurysms was excellent. One patient underwent (unrelated) cardiac surgery, all other 27 patients remained eventfree. We conclude that the same benign nature of coronary aneurysmal disease holds true for those aneurysms that develop after PTCA.