The present invention relates to a device and method for making sclerosing foam, which is useful in the treatment of varicose veins and other venous conditions. The device comprises a continuous pathway that is at least partly formed of flexible or compressible material and that comprises a foam generating structure within the continuous pathway； the foam generating structure being formed of two or more elements, wherein each element defines at least one passageway of cross sectional area 1 μm2 to 10 mm2 and said two or more elements being arranged in series； a port which allows introduction of material into or extraction of material out of the continuous pathway； and a liquid pathway that is at least partly formed of flexible or compressible material and is arranged to deliver liquid into the foam generating structure between a first and second element of the foam generating structure.
