The implantable catheter means comprises a capsula (10) having a pierceable top wall (15). A catheter (11) extending into a cavity (12) of said capsula (10) is fixed thereto by an elastomeric clamping member (30) arranged inside a connecting piece (22) which has an internal thread (23) engaged by an external thread of a pressure member (26). By turning the pressure member (26), the clamping member (30) is deformed to press against the periphery of the catheter to fix it and to seal it relative to the capsula (10). The lateral dimensions of the capsula (10) are not increased by the connecting piece (22). The catheter coupling may be easily tightened and released, and it safely prevents the catheter from being extracted.