Abstract: A retention mechanism for maintaining a position of a catheter on the connector tube of an implantable vascular access device. The retention mechanism includes an annular member dimensioned to be received over a length of the catheter when the catheter is positioned over the connector tube, and a housing for the annular member. The annular member is capable of elastic expansion for permitting passage of the member over a large diameter portion of the catheter, and elastic compression on the catheter for maintaining the position of the catheter on the connector tube. The housing has an inner passageway that includes a channel for receiving a radially outer portion of the annular member.