The title compounds, 1,3-dibenzoylimidazolidine-2-thione, C17H14N2O2S, (I), and 1,3-dibenzoyl-3,4,5,6-tetrahydropyrimidine-2(1H)-thione, C18H16N2O2S, (II), were obtained from the reactions of imidazolidine-2-thione and 1,4,5,6-tetrahydropyrimidine-2-thiol, respectively, with benzoyl chloride. Compounds (I) and (II) contain, respectively, imidazolidinethione [C=S = 1.6509 (14) A] and pyrimidinethione [C=S = 1.6918 (19) A] moieties bonded to two benzoyl rings. The molecules of (I) exhibit C2 symmetry, the C=S bond lying along the twofold rotation axis, while the molecules of (II) have mirror symmetry (Cs). The imidazolidine ring in (I) is essentially planar, while the pyrimidine ring in (II) adopts a boat conformation. Molecules of (I) are linked by weak intermolecular C-H...O interactions, while molecules of (II) are held together by van der Waals interactions.