 The selection of patients with idiopathic normal pressure hydrocephalus INPH for shunting remains difficult. The upcoming guidelines for the diagnosis and management of INPH state that there is no accepted standard for the clinical presentation, the results of imaging and the various tests that provide information on CSF dynamics 1. Hebb and Cusiamo could not find a single test that reliably predicts outcome after shunting in their systematic review of INPH 2. To properly evaluate the predictive value of diagnostic tests for the outcome of shunting all patients should receive a shunt irrespective of the test results. Only a few studies set up to examine the diagnostic reliability of tests of CSF dynamics fulfilled this condition. The common finding of these studies was that the predictive value of a positive test was high but the negative predictive values were disappointingly low. 