A coextrusion adapter for an extrusion installation with extruders and a tool for producing a composite coextrusion structure of thermoplastic material. The coextrusion adapter has a central conduit with an end at an inlet side for connecting an extruder and an end at an outlet side for connecting the tool. The coextrusion adapter has at least one coextrusion conduit with an inlet end and an outlet end. A second extruder can be connected to the inlet end. At an end facing the outlet end the adjusting elements have a wedge-shape adjusting section with one wedge surface facing the central conduit and another wedge surface facing the outlet end of the coextrusion conduit. The adjusting section of the adjusting elements is pivotal around an axis extending over the width of the outlet end by the actuating drives. When an increase of the inside diameter of the respective transverse section of the outlet end occurs the corresponding transverse section of the central conduit is narrowed, and vice versa.