An eight-membered ring consisting of alternating S and N atoms being assumed, the energy of the most likely conformations and configurations have been investigated by use of symmetry arguments and extended Hückel calculations. Theory predicts that the structure of lowest energy contains two transannular S–S bonds and this structure is that found in Nature. The theory also allows a rationalization of the structure of realgar and the reactivity of tetrasulphur tetranitride. The character of the S–N bond in S4N4, and the possible structure of S4N42+ and S4N42– are discussed briefly.