The aim of this retrospective study was to assess the value of percutaneous transluminal coronary angioplasty (PTCA) in unstable angina refractory to maximal medical therapy. The results of this procedure in these patients were compared with the results in unstable angina controlled by medication before angioplasty. Between january 1987 and january 1993, 30 patients underwent emergency PTCA for refractory unstable angina (group I). The clinical and angiographic features were compared with these of 30 patients with medically controlled unstable angina, paired for age and dilated artery (group II). The left ventricular ejection fraction was compared in the two groups (58 and 57%). The morphology of the coronary lesions according to the Ambrose classification, TIMI grading, number of lesions, degree of stenosis and severity of coronary calcification were comparable in the two groups. However, in group I, there was a significantly higher number of filling defects (30% compared with 10%, p = 0.05) and a greater number of per-PTCA complications, especially acute occlusions (23 compared with 13%, NS) with 3 deaths and 2 myocardial infarctions (compared with 1 death and 2 myocardial infarctions in group II). At long term, the restenosis, myocardial infarction and secondary death rates were comparable in the two groups with an average follow-up of 27 +/- 18 months. The poor prognosis of refractory unstable angina is therefore related to morbidity in the hospital period. These results confirm the physiopathological importance of the thrombotic process in unstable angina; the presence of "filling defect" is a poor prognostic factor associated with resistance to medical therapy. Coronary angioplasty is a valuable technique in this context but carries a higher risk of acute complications which can be reduced by an optimal platelet antiaggregant and anticoagulant therapy and in future by the use of new antithrombotic agents.