Stimulated by the recent detection of nitrosyl azide (N-3-N=O), we investigated the stability of the sulfur analogues thionitriosyl azide (N-3-N=S) and thiazyl azide (N-3=SN) by using ab initio MO calculations up to the QCISD(T)/6-311+G(d)//QCISD/6-311G(d) + ZPE level. Both azides have a similar energy content. While thionitrosyl azide is not stable with respect to Na elimination, thiazyl azide resists to this process by an energy barrier of about 110 kJ/mol. The NS and N-3 fragments resulting from homolytic cleavage Lie about 100 kJ/mol above the azides. The five-membered ring is thermodynamically much more stable than both azides but kinetically unstable with respect to cheletropic decomposition yielding N2S + N-2. Overall, trans-thiazyl azide is the most Likely candidate for experimental observation of, for example, the reaction of NS+ salts with the azide anion. IR wavenumbers of the azides were also predicted.