A system for effecting fluid-tight coupling and mechanical joinder between a medical device and a catheter tube. An elongated catheter connection stem attached to the medical device is received in the lumen of the catheter. A catheter securement collar is advanced proximally along the exterior of the catheter and connection stem inside the catheter into the assembled condition of the connection system, passing a locking ring on the interior of the securement collar over an enlargement on the distal end of the connection stem. Maximum catheter compression occurs at the locking ring, while a void internal of the catheter system is filled with an enlarged securement lip of catheter material. Distal of maximum catheter wall compression, the catheter traverses a tortuous path between the locking ring and the enlargement, around the shoulder of the enlargement, and along the adjacent surface of the enlargement.