Ostomy bag assembly having an outer bag (2) with a base plate coupling element (1) attached to an edge of an outer bag main aperture (6), and an inner bag (3) with an inner bag main aperture (7). In operation the inner bag (3) is aligned with the outer bag main aperture (6), and the inner bag (3) is provided with a liquid sealing and gas permeable barrier device (9). The three position filter device (8) is arranged to have a first, second and third operational position each allowing a different amount of gas to be guided out from the outer bag (2). A shutter member (27) is provided in movable engagement with a filter body (25) attached to the outer bag (2).
