Echocardiograms of three patients with metastatic carcinoma or lymphoma showed a sonolucent space posterior to the left ventricular epicardium, as seen in pericardial effusion. However, at surgery or autopsy no pericardial fluid was found. Instead, the pericardium was infiltrated by neoplastic tissue or fibrosis. In view of this finding, we suggest caution in the interpretation of "positive" echocardiograms for pericardial effusion in patients with neoplastic disease, especially if pericardiocentesis is being considered.