An ostomy bag having a waste-collecting chamber 20 defined by first and second walls (11,12, Fig 2), the first wall being provided with a stoma-receiving opening 32. The waste collecting chamber receives waste and/or gas from the stoma-receiving opening while a further chamber 21, acting as a gas passage, is defined in part by third and fourth walls (13, 14, Fig 2) which are connected to each other. Waste gases pass from the waste-collecting chamber through slits or perforations 40 in the third and/or fourth walls to the further chamber and then escape to atmosphere via a gas vent 61, which may be covered by a filter 30. The further chamber communicates with at least one drainage outlet 41, the drainage outlet 41 extending to one side of the stoma receiving opening and toward a bottom of the bag. A fifth wall (15, Fig 2) may provide a tortuous path inside the further chamber. Movement of the first and second walls away from each other, as a result of waste or gases entering the waste-collecting chamber, tends to move the third and fourth walls apart to at least maintain the volume of the further chamber.
