An 80-year-old man was admitted because of head trauma following a fall down a staircase. Initial CT-imaging of the brain showed only global atrophy, but repeated CT-imaging 4 days later revealed a subdural hygroma. Because of the discrepancy between the radiological deterioration and the unchanged neurological condition, we refrained from neurosurgical evacuation. Two months after the trauma, the subdural hygroma had been spontaneously resorbed, but neurological examination revealed severe residual neurological abnormalities. Subdural hygroma is a little known complication in the acute stage ofhead trauma, which is seen mainly in elderly patients. The pathophysiology is not well known. Differentiating subdural hygroma (cerebrospinal fluid (CSF) accumulation in the subdural space) from external hydrocephalus (excessive CSF accumulation in the subarachnoid space) is important in view of the therapeutic consequences. Because CT-imaging usually cannot differentiate between these 2 conditions, we recommend the use of MRI.