Chronological changes in diffuse brain swelling and brain oedema were studied in repeated CT studies following a closed head injury. These findings were compared with changes in intracranial pressure (ICP). The grades of diffuse brain swelling were classified into mild, moderate and marked according to the CT findings. Planimetry of low density areas of brain oedema was carried out on repeated CT images. Diffuse brain swelling was recognized in 71% of patients shortly after the head injury and subsided within days 3-5. Brain oedema first appeared 24 hours post injury and did not reach its maximum size and distribution before days 5-8. Thus, these two events can be clearly separated. The intracranial pressure reflected the course of the brain swelling and was not very high during the presence of maximum oedema.