We have studied the adsorption of S on the Si(001) c(4 × 2) surface by first principles total energy calculations. It is found that the first S atom is adsorbed on top of a symmetric Si dimer. Following atoms occupy similar bridge sites up to half-monolayer coverage. Increasing the amount of S atoms leads to the breaking of the underlying Si dimers. Our calculations predict that from 1/2 ML up to a full ML the growth of S is highly anisotropic. There is a preference of the S atoms to grow along the Si dimers rows. At full monolayer, all the Si dimers are broken and the surface is completely de-reconstructed with all Si atoms near bulk ideal positions.