To validate the AHCPR classification for the prognosis of unstable angina, 225 consecutive patients were recruited with a suspected diagnosis of that condition attending a tertiary hospital from November 1994 through April 1995 and followed for one year. One-hundred fifty-six (69.3%) patients were considered at high risk, 37 (16.5%) at intermediate, and 32 (14.2%) at low risk of cardiac complications. All of the patients with major in-hospital cardiac complications (8 patients) had at least one of the features of the high risk group. The high to intermediate-low hazard ratio (HR) for one-year cardiac complications after the onset of unstable angina was 4.03. Predictors of major complications (myocardial infarction or death) after the follow-up were age > 65 (HR, 5.69); diabetes (HR, 4.94); heart failure (HR, 2.65); and prolonged angina (HR, 2.55). AHCPR classification correctly identified patients with risk of severe outcomes at the hospital. Also, the classification predicted outcomes one year after hospitalization, diabetes being an important determinant of adverse cardiac events.