We present a technique to fabricate nanostructures with an atomic force microscope (AFM). By taking advantage of the AFM tip sharpness, we engrave a narrow furrow in a soft polyimide layer. The furrow is then transferred using dry etching to a thin germanium layer which forms a suspended mask. Metallic layers are then evaporated through this mask. Metallic lines with a 40 nm linewidth and single-electron transistors have been fabricated. This lift-off technique can be used on any substrate and allows easy alignment with previously fabricated structures.