Materials and Methods O-H2O-PET-CBF studies (Siemens ECAT 951/31, Erlangen, Germany) were performed in 65 patients (76 ± 13 years) with idiopathic normal-pressure hydrocephalus selected for shunt surgery based on clinical and radiological criteria and the presence of B-waves and/or increased CSF-resistance values obtained by a constant lumbar infusion test. PET-CBF studies were done before, at one week and at 7 months after VP-shunt. Clinical outcome was determined at 7 months after shunt placement by grading (scoring) the patients clinical status based on the degree of functional impairment according to the STEIN and LANGFITT scale. Thereby, patients were classified into responders (n = 33) and non-responders (n = 32). Regional specific effects in the O-H2O-uptake were assessed using statistical parametric mapping (SPM99, Wellcome Department, London, UK). An uncorrected P < 0.001 (Z > 3.09) on voxel level was selected as a threshold of significance.