The optimized geometries and energies of isolated and hydrated 6,8-dithioguanine tautomers have been studied using density functional theory and Møller–Plesset Perturbation theory implementing 6-311++G(d,p) atomic basis set. Depending on the nature of the tautomers, cyclic structures are formed where water molecules accept the NH/SH protons and donates a proton to the nitrogen or thiocarbonyl sulfur atoms. The intermolecular distances between the water molecule and the acceptor atom of 6,8-dithioguanine is about 0.5–0.7 Å longer for hydrogen bonds involving sulfur atoms. The amino group planarity has been found to be increased in the hydrated complexes as a result of hydration. The relative order of stability based on total energy of the 6,8-dithioguanine tautomers in both free and hydrated form favor the thione tautomer. The examination of molecular orbital reveals that the HOMO is localized on five-membered imidazole ring and LUMO on six-membered pyrimidine ring system. From atoms in molecules (AIM) theory an excellent linear correlation is found to exist between electron density and Laplacian of electron density with hydrogen bond length. The natural bond orbital (NBO) analysis shows a maximum charge transfer of 0.059e for O–H···S bonds and around 0.045e for S–H···O bonds.