A breast pump comprises a body member (2) including a breast engaging portion (4) shaped to engage a region of a user's breast, a container (32) attached to the body member (2), valve means (28) between the body member (2) and the container (32), and, within the body member (2), a sleeve (12) sealing the interior of the body member (2) from the atmosphere, the sleeve (12) being selectively movable from a rest condition to a displaced condition by actuating means (14) operatively connected to the sleeve (12), movement of the sleeve (12) from the rest condition to the displaced condition creating an increasing volume of reduced pressure within the body member (2) whereby firstly the valve means (28) is closed to prevent evacuation of the container (32), and whereby milk is expressed by the user into the body member (2), and return movement of the sleeve (12) from the displaced condition to the extended condition releasing the reduced pressure allowing the valve to open, the expressed milk flowing through the valve means (28) and into the container (32), the configuration of the sleeve (12) or the material of the sleeve (12) being such as to substantially prevent stretching of the sleeve (12) on movement between the rest and displaced conditions.