An electro-optical printed circuit board contains electrical conductor tracks on the one hand and optical waveguide structures on the other hand. The optical waveguide structures comprise a bottom layer, a core layer and a cladding layer. Visible areas are applied to the printed circuit board, and the core layer is applied later both to the bottom layer as well as the visible areas and structured both on the bottom layer as well as the visible areas. This structure is then transferred to the visible areas, e.g. by etching. Reference marks are thus produced which contain the information on the actual position of the optical waveguide structures.