We report continuous bilateral intracranial pressure (ICP) monitoring immediately after transtentorial herniation in a patient with massive cerebral infarction to: 1) determine presence and time course of compartmental ICP differences, and 2) to study effects of therapy on both hemispheres. A 55-year-old man admitted with watershed infarctions in the left anterior-middle-posterior cerebral arteries distribution. Initial investigations demonstrated highly narrowed left extracranial internal carotid artery. Eight days later he developed unexplained lethargy and anisocoria. Head computerized tomography (CT) showed massive left hemispheric infarction, edema, and midline shift. Bilateral subarachnoid bolts demonstrated equally elevated ICP in both hemispheres. Hyperventilation and osmotic therapy produced near-identical ICP reduction bilaterally with resolution of anisocoria. Later, plateau waves and autonomic instability developed. Shortly before loss of brainstem function, interhemispheric ICP gradients (left greater than right) of 30–40 mm Hg developed. Intracranial pressure did not equalize prior to brain death determination. Bilateral ICP monitoring did not reveal an interhemispheric ICP gradient soon after transtentorial herniation in massive MCA infarction. The presence of interhemispheric ICP gradients in massive stroke remains unproven and further clinical study is necessary.