We assessed the 90-day prognostic value of stress tests and C-reactive protein (CRP) after medical stabilization of unstable angina. We included 139 consecutive patients with unstable angina who were free of complications or did not undergo revascularization during hospitalization. Blinded CRP assays and a stress test (95 exercise electrocardiograms, 44 dobutamine echocardiograms) were performed within the first week after discharge. Of 139 participants, 44 (31.6%) had an ischemic stress test response. CRP was elevated (> 1.5 mg/dl) in 40 patients (28.7%). CRP >1.5 mg/dl was more frequently observed among patients who experienced death or myocardial infarction at 90 days (88.2% vs 20.5%, p <0.0001). Compared with the stress tests, CRP showed greater sensitivity (88% vs 47%) and specificity (81% vs 70%) for increased risk, and higher positive (37.5% vs 18.2%) and negative (98% vs 90%) predictive values. The area under the receiver operating curve of the relation with the 90-day outcome increased from 0.58 +/- 0.07 to 0.83 +/- 0.05 when the CRP data were added to the stress tests results (p <0.001). Elevation of CRP differentiated stress tests negative patients with increased risk of major events during follow-up. In patients who respond to medical treatment for unstable angina, CRP elevation may be a better parameter than the stress test in identifying the presence of persistent plaque instability.