We report on an alternative approach for the fabrication of metallic nanostructures: a selective growth on silicon substrates patterned by local anodic oxidation using atomic force microscopy. Our method represents a maskless, four-step process which combines a top-down and bottom-up approach. The dimensions of both the oxide lines and metallic elements can be controlled during the technological process. In this paper we demonstrate the preparation of gallium and cobalt structures on silicon substrates but this method can be extended to other combinations of metals and substrates enabling thus the fabrication of ordered nanostructures of various compositions and properties on locally oxidized surfaces.