A multi-layer headbox for a paper or board machine including stock inlet headers each providing one stock and coupled to a tube bank which in turn is coupled to a respective intermediate chamber. The stock flows from the intermediate chambers into a turbulence generator and through pipes in the turbulence generator into a slice cone to be discharged therefrom onto a forming wire. The multi-layer headbox includes distribution valves for regulating the flow of dilution water across the width of the headbox. Each distribution valve communicates with a distribution plate placed in connection with the tube bank. From each valve, the dilution liquid is distributed at the same time to all the stocks that form the different layers of the web in the multi-layer headbox at a specific position of width of the multi-layer headbox.