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 (1) comprises a continuous pathway (2) that is at least partly formed of flexible or compressible material and that comprises a foam generating structure (7) within the continuous pathway (2)； the foam generating structure (7) being formed of two or more elements (8, 9), wherein each element (8, 9) defines at least one passageway of cross sectional area 1µm2 to 10mm2 and said two or more elements (8, 9) being arranged in series； a port (12) which allows introduction of material into or extraction of material out of the continuous pathway (2)； and a liquid pathway (5) that is at least partly formed of flexible or compressible material and is arranged to deliver liquid into the foam generating structure (7) between a first (8) and second element (9) of the foam generating structure (7).
