In 857 consecutive patients with acute myocardial infarction (AMI), the occurrence of chest pain more than 24 h after hospital admission is described and related to death or reinfarction during one year of follow-up. Prolonged chest pain was observed in 333 patients (39%). In this group 15% died and 7% developed reinfarction during the first month as compared with 10%(p < 0.05)and2%(p < 0.01) respectively in patients without prolonged pain. However, during one year of follow-up mortality did not differ significantly between patients with (27%) and without (24%) prolonged pain. The 1-year reinfarction rate was similar in the two groups (18% and 14 %, respectively; NS). We conclude that AMI patients with prolonged chest pain have a particularly high mortality during the first month. However, during a longer follow-up the prognosis is similar in patients with and without prolonged chest pain.