Neurological and vascular complications of Arnold-Chiari malformation treated with ventriculoatrial shunting may result in sudden or unexpected death. Two patients with Arnold-Chiari malformation and ventriculoatrial shunting had variable clinical manifestations and diagnostic difficulties. A 3-year-old girl with a 1-day history of right-sided heart failure died unexpectedly soon after cardiac catheterization. At autopsy examination an adherent thrombus around the ventriculoatrial catheter tip, pulmonary infarction, and embolic pulmonary arterial hypertensive changes were found. In the second case, a 21-year-old man died suddenly after a brief episode of dyspnea. He had a 1-year history of "asthma" before death. Autopsy examination confirmed pulmonary infarction and embolic pulmonary arterial hypertensive changes. There was no histological evidence of asthma. Deaths in both cases were due to pulmonary infarction stemming from thromboemboli derived from ventriculoatrial catheterization. Both patients had evidence of long-standing clinically unsuspected vascular disease, which may have contributed to death. Cardiac catheterization may also have precipitated death in the first patient. Other possible problems leading or contributing to sudden death in such patients include pulmonary hypertension with chronic cor pulmonale, airway obstruction from recurrent laryngeal nerve paralysis, and shunt blockage with acute hydrocephalus. Lethal brainstem compression may also accompany relatively minor trauma associated with chronic cerebellar tonsillar herniation in these patients.