Cortical biopsies of eight patients with craniocerebral trauma complicated with subdural or epidural hematoma were examined with the transmission electron microscope. The patients showed post-traumatic neurobehavioural disorders and moderate or severe vasogenic brain edema. The capillary wall displayed increased vacuolar and vesicular endothelial transport, basement membrane thickening and vacuolization and swollen astrocytic end-feet. Pericapillary and parenchymatous hemorrhages were also observed. The extracellular space appeared considerably enlarged with presence of proteinaceous hematogenous edema fluid and fibrinous organization. Pyramidal and non-pyramidal neurons showed intracellular edema featured by irregular enlargement of rough endoplasmic reticulum, nuclear envelope and Golgi apparatus. The myelinated axons exhibited clear or black type axoplasmic degeneration, varicose fiber swelling, myelin sheath distortion, formation of myelin ovoids and increased amount of oligodendroglial ad-axonal layer. The dendrites also showed clear or dark and beaded shape degeneration. Synaptic degeneration was characterized by swollen and shrunken pre- and postsynaptic endings, clumping, enlargement and depletion of synaptic vesicles, synaptic membrane complex disassembly and detachment of glial ensheathment. Perivascular and perineuronal astrocytes appeared remarkably swollen. Phagocytic astrocytes were also found. Oligodendrocytes displayed hydropic and reactive changes. Reactive oligodendrocytes induced myelinolysis. The brain barrier dysfunction, the vasogenic and cytotoxic edema and the subsequent neuronal and neuroglial cell reactive and degeneration processes might represent the morphological substrate responsible for the post-traumatic neurobehavioural disorders.