OBJECTIVE To determine whether excision of complex, ulcerated plaque improves the risk of patients with unstable angina to the level of those with stable angina, the results of directional coronary atherectomy were compared in patients with these two syndromes. BACKGROUND The procedural results of angioplasty in the setting of unstable angina are not as favorable as those observed for chronic stable angina, presumably because thrombus-associated plaque augments the risk of abrupt closure. METHODS Two hundred eighty-seven consecutive patients who had undergone directional atherectomy for a single new stenosis were studied. Seventy-seven patients had stable angina (Group I); 110 patients had progressively worsening angina in the absence of rest or postinfarction angina (Group II); and 100 patients had rest or postinfarction angina, or both (Group III). RESULTS Major ischemic complications (death, Q wave infarction, emergency bypass surgery) occurred more frequently in Group III (1.3% [Group I] vs. 0.9% [Group II] vs. 7% [Group III], p = 0.036). This difference was largely due to a higher incidence of emergency surgery in Group III (1.3% [Group I] vs. 0% [Group II] vs. 5% [Group III], p = 0.05). Clinical follow-up was obtained in 97% of successful procedures for a mean follow-up period of 22 months (range 9 to 52) and revealed a higher incidence of hospital admission for angina (p = 0.05) and a trend toward more bypass surgery (p = 0.09) and myocardial infarction (p = 0.16) in Group III. There was no difference in repeat percutaneous interventions among the three groups (range 19% to 24%, p = 0.75). CONCLUSIONS These results show that the definition of unstable angina is important in determining the immediate outcome of directional atherectomy. In the absence of rest or postinfarction angina, the immediate results are not significantly different from those obtained in stable angina. Our results also suggest that both the immediate and short-term outcome in unstable angina are not greatly influenced by atherectomy but more so by the pathophysiology of unstable angina, which increases the complications of percutaneous interventions.