That blood in the subarachnoid space could possibly produce hydrocephalus was first suggested by Bagley in 1928 (3, 4). His conclusions were based on both experimental and clinical studies even though he actually failed to demonstrate a communicating hydrocephalus. Subsequent workers have repeatedly demonstrated leptomeningeal thickening associated with blood in the subarachnoid space from a variety of causes (8, 9). Recently neurosurgeons have become more aware of this pathological and clinical entity and have reported excellent results in patients treated soon after its recognition (5,9,16). We report a single case of post-subarachnoid haemorrhage hydrocephalus which we feel serves to emphasize the dramatic improvement which can follow treatment of the hydrocephalus.