Catheter Insertion Needle (3.5 mm in diameter) including Sleeve, Cannula and Stylet accomodating catheters of 2.6 mm. The outer cannula has an open slit which allows it to be withdrawn after insertion of the catheter. The inner cannula allows fluid to be drained from the target area when appropriate. A luer type conical fitting in the cannula knob facilitates aspiration. The stylet is used to seal the inner cannula during insertion into the brain.