In 333 (94%) out of 356 patients, who underwent successful TCA between October 1977 and June 1983, follow-up angiograms were performed. A total of 439 follow-up angiograms taken at 1-48 (on average 5.6) months after successful angioplasty were analysed. Restenosis rate was 12% if defined as remaining luminal widening of less than 20% compared to the situation before angioplasty. Its rate was 16% if defined as loss by at least 50% of the initial increase in luminal diameter. Restenosis rate was 17% if according to the international registry of the NHLBI defined as either loss by at least 50% of the initial increase in luminal diameter or as an increase in post-TCA-stenosis by at least 30%. When excluding those patients with restenosis who underwent repeat TCA and those with dilatation of an aortocoronary bypass stenosis the restenosis rate was reduced to 15.4%. In these two subgroups restenosis rate was 33% and 45%, respectively. Several factors may be responsible for the observed relatively low restenosis rate: Selection of patients Technique of TCA Medical treatment during and after TCA Reduction of risk factors, compliance of patients Unknown factors. Chronical medical treatment with high doses of acetylsalicylic acid, nitrates, and calcium blockers are considered most likely to be responsible for this result.