One hundred ninety-six consecutive patients admitted to the coronary care unit with suspected unstable angina were classified clinically as having either definite (113 patients) or suspected unstable angina (83 patients) within 24 hours of admission. Patients were followed prospectively to determine their outcome in the hospital and in the first 4 months after discharge. Three patients had a non-fatal myocardial infarction in the hospital and 2 died (1 fatal myocardial infarction, 1 death immediately after coronary bypass surgery). During follow-up (mean 4.2 +/- 2.3 months), 6 additional patients had a nonfatal myocardial infarction, 4 died and 22 were readmitted with definite unstable angina. The incidence of nonfatal infarction or death was significantly lower in patients with suspected unstable angina during both the primary hospital admission (0 of 83 vs 5 of 113, p less than 0.05) and after discharge from the hospital (1 of 83 vs 9 of 113, p less than 0.05), and fewer patients with suspected unstable angina were readmitted with a recurrence of definite unstable angina (1 of 83 vs 21 of 113, p less than 0.001). Thus, a simple clinical classification into definite or suspected unstable angina performed within 24 hours of admission to the coronary care unit identified a substantial group with a low short-term risk of adverse events.