Apparatus for delivering therapeutic agents to the central nervous system of a subject is described. The apparatus comprises at least one intracranial catheter and a percutaneous access device. The percutaneous access device comprises a body having at least one extracorporeal surface and at least one subcutaneous surface, the body defining at least one port for connection to an implanted intracranial catheter. The port is accessible from the extracorporeal surface of the device, but is provided with a seal such as a rubber bung between the lumen of the port and the extracorporeal surface. The percutaneous access device may have more than two ports and/or a flange. A method of implanting the percutaneous access device is also described.