Twenty-nine patients who were referred with the possible diagnosis of constrictive pericarditis underwent electrocardiographically gated transverse spin-echo magnetic resonance (MR) imaging to determine the accuracy of spin-echo MR imaging for the diagnosis of constrictive pericarditis and to compare the morphologic features of constrictive pericarditis with those of restrictive cardiomyopathy as seen on spin-echo MR images. Constrictive pericarditis was verified by means of surgery and/or catheterization in 17 patients. The sensitivity, specificity, and accuracy of MR imaging in the diagnosis of constrictive pericarditis were 88%, 100%, and 93%, respectively. Thickened pericardium was observed in 88% of patients with proved constrictive pericarditis. Pericardial thickening was not identified in patients with restrictive myocarditis (n = 4). The most frequent site of pericardial thickening was over the right ventricle. In constrictive pericarditis, the signal intensity of the thickened pericardium was similar or decreased compared with that of the myocardium. Indirect findings of impaired right ventricular diastolic filling (eg, dilatation of the inferior vena cava and right atrium) were identified in constrictive pericarditis and restrictive cardiomyopathy. MR imaging can serve as a noninvasive examination for the definitive diagnosis of constrictive pericarditis and can help distinguish between constrictive pericarditis and restrictive cardiomyopathy on the basis of pericardial thickness.