OBJECTIVE To evaluate the incidence and the clinical significance of pericarditis in the acute myocardial infarction. METHODS Retrospective study. METHODS The Coronary Care Unit of a University Hospital. METHODS We have studied 668 consecutive patients with their first acute myocardial infarction admitted at the Coronary Care Unit, Hospital General de Galicia, Santiago de Compostela, Spain, in the years 1983 to 1988. Pericarditis was defined as the presence of a pericardial friction rub on auscultation during the hospital course. Pericarditis was noted in 86 patients (12.8%), who were considered as group A. The remain 582 patients were considered as group B. Statistical analysis was carried out using the BMDP statistical package. RESULTS Pericarditis occurred in 12.8% of the patients. Patients with, compared to those without, pericarditis had a lower age (59.0 +/- 12.4 years; p = .0005), and a higher percentage of males (86.1% versus 75.6%; p = .038), an a higher percentage of smokers (63.9% versus 48.6%; p = .01). The delay to the hospital admission was greater in group A (12.6 +/- 18.5 hours versus 8.0 +/- 11.7 hours; p = .0024). Pericarditis more often occurred in the setting of anterior wall myocardial infarction and in Q-wave infarct. The group A had a higher CPK peak (1877.5 +/- 1548.9 UI/L versus 1240.2 +/- 961.5 UI/I; p = .001) and a higher peak of CK-MB (213.7 +/- 134.7 UI/L versus 160.8 +/- 112.9 UI/L; p = .001). In-hospital mortality was significantly lower in group A (6.9% versus 17.2%; p = .016). The multivariate analysis by stepwise logistic regression identified the Q- wave myocardial infarct, the age, the delay to the hospital admission, the peak of MB creatine kinase and location of infarct as the only independent predictive variables for the pericarditis occurrence. CONCLUSIONS We conclude that the pericarditis in the setting of Q-wave myocardial infarction, with anterior wall location, and is related to transmural extension of the myocardial necrosis.