Although viewed as promising drug candidates, few efforts have been addressed towards the structural chemistry of 2-hydrazonothiazolidin-4-ones. Therefore, 2-[(3-phenylsulfanylpropylidene)- hydrazono]thiazolidin-4-one (ATZ3) was synthesized and its crystal and molecular structure was studied by NMR and X-ray single crystal diffraction. The 1H NMR spectral data indicated that the hydrazone group assumes the Econfiguration, which was further confirmed by bi-dimensional NMR and crystallographic data. Despite agreement between most bond lengths and angleswith their expected values, the crystalline packing provided important information with regard to the double bond position involving the C-4 carbon. Quantum chemical calculations at Semiempirical, Density Functional Theory (DFT) and Ab Initio levels provided a good agreement between calculated and structural results provided by X-ray analysis. The system’s dimerization energies were also estimated. Statistical and Hierarchic Cluster Analysis (HCA) revealed interesting aspects of the calculations and pointed to the B3LYP as the most accurate in the determination of structure among the methods considered, in spite of some good results achieved by semiempirical schemes.