To assess the results of a conservative coronary angioplasty strategy in unstable angina pectoris, the records of 1,421 consecutive patients without previous myocardial infarction undergoing a first percutaneous transluminal coronary angioplasty (PTCA) between 1986 and 1990 were reviewed. Of these patients, 631 had unstable and 790 had stable angina pectoris. Only after an intense effort to medically control symptoms, the unstable patients underwent PTCA at an average of 15.4 days (range 1 to 76) after hospital admission. Primary clinical success was achieved in 91.7% of patients with unstable and in 94.4% of those with stable angina pectoris (p = not significant). In-hospital mortality rates were 0.3 and 0.1%, respectively (p = not significant). Nonfatal in-hospital event rates for acute myocardial infarction, cerebrovascular accident and coronary bypass surgery were only slightly higher in patients with unstable angina pectoris; however, the difference from the stable group was significant when all events were combined (9 vs 5.9%; p less than 0.04). During 6-month follow-up, no significant difference in adverse events was found between the groups. The respective rates for the unstable and stable groups were 0.4 and 0.2% for death, 5.5 and 5.1% for major nonfatal events, and 17.7 and 20.1% for repeat PTCA. These results suggest that use of a conservative PTCA strategy in the treatment of patients with unstable angina pectoris results in favorable and similar immediate and 6-month outcomes compared with those in patients with stable angina pectoris.