Brain oedema is defined as an abnormal accumulation of fluid in the brain tissue accompanied by an increased volume of the brain. It results in the intracranial hypertension directly endangering the patient’s life. No causal treatment of the brain oedema is known at present. The brain oedema is not a disease, but it is a symptom of various clinical states. That is why experimental studies of its pathophysiology become the centre of attention. Though the classification of brain oedema according to the pathogenesis is still used (the vasogenic type - resulting from the increased permeability of blood-brain barrier; the cytotoxic type - caused by the cell metabolism impairment), recent papers has shown a definite retraction from such categorisation. It has been shown that neither type of brain oedema comes alone, but both can occur simultaneously during the development of the pathological state of the brain. The most important appears to be the primary insult. It affects the state of blood-brain barrier and brings about the vasogenic extracellular oedema or it can influence the cell metabolism with subsequent cytotoxic, cellular oedema. Categorisation of oedema into extracellular and cellular reflects more precisely the impairment of the homeostasis of the internal environment of the brain.Contemporary viewon the classification and pathophysiologicalmechanisms of the brain oedema is discussed in our review.

        Key words: intracranial hypertension, brain oedema, internal environment of the brain.