A midline rupture of the mesencephalon was found in 3 young males surviving closed head injury for 3-5 days. Other brain damage was relatively mild, but there was brain oedema with signs of herniation. In only one case were there symptoms of a hypothalamic lesion. The author suggests that a rupture is initiated by the compression of the brain stem against the clivus, whereby the pedunculi are displaced away from each other, and that the rupture naturally continues along the midline vessels to end in the aqueduct.