We evaluated eight patients with possible or probable paradoxical cerebral embolism. One patient had a hemispheric transient ischemic attack; the others had infarcts. Ischemic symptoms followed a Valsalva's maneuver in three cases. Others were linked to placement of a Swan-Ganz catheter, deep venous thrombosis and pulmonary embolism, right atrial myxoma, and use of oral contraceptives. Four had no known predisposing conditions. In six patients, contrast echocardiography showed right-to-left shunting. Cardiac catheterization showed a patent foramen ovale in three patients; one had an atrial septal defect. In the clinical setting of otherwise unexplained cerebral embolism in a young patient, paradoxical cerebral embolism should be considered. Contrast echocardiography is a useful screening test for this purpose.