We present a new lithographic technique with a scanning tunneling microscope (STM), allowing us to pattern thin evaporated Au films at the nanometer scale. The electron beam produced by the STM tip is used to expose a very thin layer of ω-tricosenoic acid. Only four monolayers of the acid, which acts as an electron sensitive, negative resist, are deposited on top of the Au films using the Langmuir-Blodgett technique. We have verified the influence of the exposure conditions on the quality of the fabricated fine-line structures with a linewidth down to 15 nm. We can also measure the electrical properties of narrow Au lines which interconnect large predefined contact pads. As expected, the low-temperature magnetoresistance is strongly influenced by quantum interference effects.