Since extensive studies of constrictive pericarditis by CT have not been reported, we performed a plain and contrast enhanced CT on 4 patients of constrictive pericarditis diagnosed by cardiac catheterization or echocardiography and confirmed at the time of surgical operation. The CT findings were as follows: The normal pericardium was smooth, could be visualized in the right and anterior regions of the heart, and was approximately or less 2 mm in thickness. On the other hand, the pericardium in constrictive pericarditis was irregularly thickened, was visualized even in the left and posterior regions of the heart, and was more than 2 mm in thickness. The mean CT value of the pericardium in constrictive pericarditis was significantly increased as compared with that of the normal pericardium. The contrast enhanced CT image revealed a marked dilatation of superior and inferior caval veins (SVC and IVC) even in the cases with normal size of each cardiac chamber. The ECG gated CT performed on one case demonstrated the impaired ventricular expansion. After pericardiectomy, the ventricular chambers showed a tendency to dilate, and the dimension of the SVC and IVC were reduced. Thus, CT is thought to be a useful noninvasive technique in evaluating the thickness of the pericardium, its pathology and the degree of dilatation in each cardiac chamber or the vena cavae.