This study has followed up the natural history of postischemic inverted T waves and assessed the prognosis. 40 consecutive patients with unstable angina with postischemic precordial inverted T waves in the noninfarcted, previously ischemic area were followed during the persistence (negative T wave period) and after resolution of inverted T waves (positive T wave period). The outcome with frequencies of acute myocardial infarction, acute ischemic syndrome, angina pectoris, positive exercise test, silent myocardial ischemia, anterior wall motion abnormalities on echocardiogram, positive coronary arteriography were determined and compared in the negative versus positive T wave periods. Postischemic inverted T waves showed resolution within the postischemic 3-21 days (at a mean of 10.6 days) in 31 patients on medical treatment alone during the whole study period. Frequencies of parameters/patients determined in negative versus positive T wave periods are as follows: acute myocardial infarction: 5/40 versus 0/31 (non significant), acute ischemic syndrome: 25/40 versus 2/31 (p < 0.001), angina pectoris: 32/40 versus 11/31 (p < 0.001), positive treadmill exercise test: 14/16 versus 14/30 (p < 0.02), silent myocardial ischemia: 14/14 versus 16/31 (p < 0.01), hypokinesis 26/34 versus 4/24 (p < 0.001), positive coronary arteriography: 4/4 versus 11/11 (non significant). In most patients on medical treatment, the postischemic inverted T waves tend to resolve within 3 weeks. Attention has to be paid to the patients with postischemic inverted T waves during the negative T wave period: the high ischemic risk gradually decreases with resolution of negative T waves.