OBJECTIVE: To assess how clinical and angiographic findings are related to the decision to carry out coronary angioplasty (PTCA) or coronary bypass grafting in patients with multivessel coronary artery disease. DESIGN: Prospective survey carried out in 14 centres in the Lombardia region of Italy. PATIENTS: 1468 consecutive patients under going coronary arteriography for known or suspected ischaemic heart disease between May and October 1994, who were found to have multivessel coronary artery disease. MAIN OUTCOME MEASURES: Multivariate analysis was undertaken using stepwise logistic regression to identify the clinical and angiographic variables correlated with revascularisation (v medical treatment) in all of patients, and with surgery (v angioplasty) in the subset of revascularised patients. RESULTS: In all patients the clinical decision after coronary arteriography was made by physicians of each participating centre on the basis of their experience and clinical judgment: 53% of patients had bypass surgery, 28% had PTCA, and 19% continued medical treatment. The choice of a revascularisation procedure was directly related to a clinical diagnosis of unstable angina (P < < 0.001), the presence of left anterior descending artery disease (P < < 0.001), and to an ejection fraction > or = 40% (P < < 0.001), and inversely related to history of previous coronary bypass surgery (P < < 0.001). In revascularised patients, bypass surgery was the preferred treatment in patients with left anterior descending artery disease (P < < 0.001), three-vessel disease (P < < 0.001), and in those with at least one occluded vessel (P = 0.008). The choice of PTCA was significantly related to history of previous PTCA (P < < 0.001) or coronary bypass surgery (P < < 0.001), to a clinical diagnosis of non-Q wave myocardial infarction (P = 0.002), and to the possibility of implanting an intracoronary stent (P = 0.01). CONCLUSIONS: Bypass surgery is still the most widely used treatment for patients with multivessel coronary artery disease. This analysis provides a basis for comparison with future developments in the treatment of such patients. Further advancements in PTCA technology are needed to tilt the balance in favour of this less invasive procedure.