To prevent cerebral vasospasm after aneurysmal subarachnoid haemorrhage, cisternal irrigation has been reported to be more effective when combined with continuous head-shaking (head-shaking method). The present study was conducted to evaluate the safety and preventative effect for vasospasm in patients treated with the head-shaking method. Six of 17 patients managed postoperatively by the original head-shaking procedure developed neurological deterioration related to the method: two had intracranial haematoma (one with acute interhemispheric subdural haematoma, and the other with cerebellar haemorrhage), two had acute brain swelling, and two failed to show abnormal findings on computed tomography. These pathological processes may be suitably referred to as "head-shaking syndrome". Delayed ischaemic neurological deficits associated with low-density lesions on computed tomography were demonstrated in five patients (29%). From these observations, the head-shaking method may not be as safe as described in the original articles, and is critically evaluated in terms of its preventative effect for cerebral vasospasm.