The invention relates to a connection device for a catheter, especially for a peripheral venous catheter, comprising a main body (1) with a main body infusion channel (2) and a through-flow element (7a, 7b, 7c) having sterilizing effect and extending in the form of a bag in flow direction of the main body infusion channel (2), and is characterized in that an attachment body (10) having an attachment body infusion channel (16) is detachably fixed to the main body (1) and the through-flow element (7a, 7b, 7c) extends at least also into the attachment body infusion channel (16) and is mounted displaceably in the longitudinal direction of the main body infusion channel (2).
