The deposition of Pt onto unreconstructed Au(111) and Au(100) was studied with cyclic voltammetry and in-situ STM. The latter revealed that in [PtCl4](2-) containing electrolytes, both surfaces are covered by an ordered adlayer of the complex. For the adsorbed [PtCl4](2-) a slightly compressed (root7 x root7) R19.1degrees-structure was assumed for Au(111) and a (3 x root10) for Au(100). In both cases, a rather high overpotential for Pt deposition was observed, most probably due to the high stability of the [ptCl(4)](2-) complex. Nucleation of Pt starts mainly at defects like step edges for low deposition rates and three-dimensional clusters are formed. Due to the high overpotential, some nuclei appear also on terraces at random sites. Higher coverages of Pt lead to a cauliflower like appearance. It is not possible to dissolve the platinum clusters at positive potentials without severely roughening the gold surface. The [PtCl4](2-) complex is oxidized to the [PtCl4](2-) complex at about 0.7 V, when metallic Pt is on the surface.