Abstract Using ab initio calculations, based on the density functional theory, we have investigated the electronic, magnetic and structural properties of a Mn neutral impurity on the bare and hydrogenated Si(1 0 0) surface, as well as on bulk Si. We have observed that the most stable site for adsorption on the bare surface is near the second layer, below a substrate dimer, whereas for the hydrogenated surface it is in the through, between two dimer rows. Hydrogenation makes the surface less reactive and increases the formation energy of the impurity in the surface. In the bare surface, we have found a substitutional site that has the same formation energy as an interstitial one, and this can be an important route for the development of dilute magnetic semiconductors based on Si.