X-Ray diffraction analysis was used to establish the molecular structures of some adducts of benzoyl isothiocyanate with hydrazones: benzaldehyde 4-benzoyl-2-phenylthiosemicarbazone (1), 2-benzoylimino-3,5-diphenyl-2,3-dihydro-1,3,4-thiadiazole (2), and 5-benzoylimino-2,2-dimethyl-4-phenyl-1,3,4-thiadiazolidine (3). In adducts 2 and 3, a strong intramolecular interaction between sulfur and carbonyl oxygen atoms has been found. The S…O distance is 2.56 Å for 2 and 2.76 Å for 3, and the oxygen atom lies approximately in the plane defined by the sulfur atom and the two carbon atoms bonded to the sulfur atom. The absence of a characteristic absorption due to a carbonyl group in the IR spectra of 2 and 3 reflects the intramolecular interaction. The crystal of 1 is triclinic, space group P\barl, with a=12.041, b=8.414, c=11.298 Å, α=116.13, β=103.39, γ=103.27°; that of 2 is monoclinic, space group P21/c, with a=20.842, b=3.977, c=21.120 Å, β=103.55°; and that of 3 is monoclinic, space group P21 with a=12.559, b=6.910, c=10.283 Å, β=115.46°. The structure has been refined by the block-diagonal least-squares method to R=0.089 with 2508 reflections for 1, to R=0.088 with 1872 reflections for 2, and to R=0.098 with 1031 reflections for 3.