Only a part of the patients suffering from thrombosis of cerebral veins and sinuses show signs of raised intracranial pressure, pareses and seizures. More often these patients present with headaches only, even with delayed epilepsy or psychoses. If the results of CT examination are doubtful or normal in these cases, a detailed history of present illness and careful investigation of cerebral spinal fluid are of great importance. Pleocytosis without further cytological specification is not sufficient to make the diagnosis of encephalitis. Another risk of wrong diagnosis results from the misinterpretation of CT findings and omission of angiography.