We have used first-principles calculations to study the structural, electronic, and thermodynamic properties of the three known forms of Rh-S chalcogenides: Rh(2)S(3), Rh(3)S(4), and Rh(17)S(15). Only the first of these materials of interest for catalysis had been studied previously within this approach. We find that Rh(17)S(15) crystallizes in a Pm3m centrosymmetric structure, as believed experimentally but never confirmed. We show band structures and densities of states for these compounds. Finally, we also investigated the ground-state structure of solid sulfur (alpha-S), one of the few elements that represents a challenge for full first-principles calculations due to its demanding 128-atom unit cell and dispersion interactions between S(8) units.