The formation and stripping of a cobalt adlayer were studied by electrochemical techniques at underpotential conditions, monitoring the deposition/dissolution onto/from a polycrystalline gold electrode. The kinetics of the former process fit a model where adsorption and diffusion-controlled two-dimensional instantaneous nucleation of cobalt occurs simultaneously onto the gold electrode surface. The latter involves a complex mechanism where adsorption/desorption competes with two processes, an instantaneous nucleation and growth of two-dimensional holes under charge transfer control and a progressive one. However, it was found that the relative contribution of the instantaneous nucleation was the most important independently of the applied potential.