Some clinicians have challenged the clinicopathologic correlation in patients with brain herniation from acute mass lesions. Earlier studies have questioned the significance of downward displacement of the brainstem in supratentorial herniation. Using recent generation MRI, we studied a patient with an acute hemorrhagic infarction. MRI demonstrated significant compression of the diencephalon with downward displacement of the midbrain and hyperintensity on T2-weighted sequences in the lateral mesencephalon during progression from early diencephalic stage to midbrain upper pons stage of herniation. This is the first intra vitam documentation of diencephalic herniation by MR imaging and confirms rostrocaudal deterioration usually found at autopsy.