The astrocytic changes and reactivity in human brain trauma complicated with subdural haematoma or hygroma have been analysed in nine patients. Cortical biopsies of frontal, temporal and parietal regions were examined with light and transmission electron microscopy. At light microscopy level oedematous clear and dense astrocytes, binucleated and multinucleated astrocytes and hypertrophic reactive astrocytes were distinguished in either moderate or severe vasogenic brain oedema. Swollen, clear and dense perineuronal astrocytes were observed compressing and indenting dark, degenerated pyramidal and non-pyramidal nerve cells. At electron microscopy level glycogen-depleted and glycogen-rich astrocytes were found in some patients. Dense and reactive hypertrophic astrocytes exhibited increased amounts of dilated smooth endoplasmic reticulum, microtubules, lipofucsin granules, gliofilaments and alpha type glycogen particles. In severe oedema the astrocytic ensheathment of synaptic contacts is lost, the perivascular astrocyte end-feet appeared dissociated from the capillary basement membrane and the interastrocytary gap junctions are disrupted. The posttraumatic neurological deficits and the neurobehavioural disorders of the patient studied are correlated with astrocyte ultrastructural changes and blood brain barrier disruption.