Temperature stable polymer optical waveguides have been realised and integrated into printed circuit boards (PCBs). A special waveguide fabrication process has been developed which is compatible with standard PCB processing technologies. Multimode waveguides with a 100 × 100 µm² cross-section have been produced by hot embossing thin polymer foils. Embedding of the waveguide foils into multilayer PCBs has led to a hybrid electrical-optical circuit board solution.