A system (2) for removing radon (4) from a drainage system that comprises a number of drainage pipes (6) arranged under a building (20) is disclosed. The drainage pipes (6) are in fluid communication with a collecting well (8). The collecting well (8) is arranged outside the building (20) and that a ventilator (10) is provided in the collecting well (8), wherein the ventilator (10) is connected to a drainage pipe (6) that extends into the collecting well (8).