Described is an apparatus (1) for extruding plastic material for hollow bodies comprising: a frame (2); an outer extrusion body (3); an inner extrusion body (4) designed to be contained inside the outer body (3) and having a housing cavity (5) forming an annular lip (6); said inner body (4) and outer body (3) forming an annular extrusion cavity (7) designed to be touched by plastic material; a supporting body (8) designed to be housed in the housing cavity (5); first adjusting means (9) and second adjusting means (10) designed to deform said inner body (4) at the lip (6) so as to adjust the relative position between the lip (6) and the outer body (3).