For many years percutaneous needle and classic burr-hole trephination with insertion of plastic catheters for external ventricular drainage are in use. The shortcomings of the conventional puncture needles were compensated for by the development of a modified instrument in recent years. In this prospective study we tried to define advantages and disadvantages of percutaneous ventriculostomy with this modified needle in a large number of patients. We treated and followed a total number of 200 patients with external ventricular drainage for various reasons (42% obstructive hydrocephalus, 27% haematocephalus, 11% malresorptive hydrocephalus, 11% elevated ICP and 9% infections). The ventriculostomy is performed--after percutaneous trephination with a 1.5 mm drill and 1.2 mm needle under local anaesthesia as a bedside procedure. The modified blunt needle is provided with markings and a set screw which allows insertion to a prefixed depth and a sharp guide which is withdrawn after penetration of the dura. It is then bent rostrally and fixed by a plaster cast. The mean duration of drainage was 9 days (1-30 days). Mean operating time for the whole procedure including fixation and connection to the drainage system was 20 minutes. Overall complication rate was 13% (N = 26). Two intracerebral haemorrhages (1%) occurred, of which one was caused by overdrainage. Five (3%) infections in primarily not infectious cases (N = 182) were seen. Only one case of infection occurred without loosening of the needle on day 17. In 19 patients (10%) the needles had loosened. Fifteen times this complication was repaired in time and no infection occurred.(ABSTRACT TRUNCATED AT 250 WORDS)