In each of the four title compounds, namely (Z)-5-benzylidene-2-thioxothiazolidin-4-one, C10H7NOS2, (I), which crystallizes with Z' = 2 in space group P2(1)/n, (Z)-5-(4-methylbenzylidene)-2-thioxothiazolidin-4-one, C11H9NOS2, (II), (Z)-2-thioxo-5-[4-(trifluoromethyl)benzylidene]thiazolidin-4-one, C11H6F3NOS2, (III), and (Z)-5-(4-methoxybenzylidene)-2-thioxothiazolidin-4-one, C11H9NO2S2, (IV), there is a very wide C-C-C angle (ca 130 degrees ) at the methine C atom linking the two rings. Pairs of N-H...O hydrogen bonds link the two independent molecules in (I) into a cyclic dimeric unit, and these units are further linked into complex sheets by three independent C-H...pi(arene) hydrogen bonds. The molecules of (II) are linked by paired N-H...O hydrogen bonds into centrosymmetric R(2)(2)(8) dimers; the molecules of (III) and (IV) are linked into chains of rings, which are constructed from a combination of N-H...S and C-H...O hydrogen bonds in (III), and from a combination of N-H...O and C-H...S hydrogen bonds in (IV).