The X-ray structure of the 1:1 co-crystal (1) between the antibacterial drug sulfadimidine (SD) and p-chlorobenzoic acid (PCL) is reported. Compound 1 crystallizes in the space group P2₁/c with a = 15.354(5)Å, b = 14.433(4)Å, c = 18.732(5)Å, β = 94.540(5)°, and Z = 8. In the two independent co-crystal units, identical R₂²(8) hydrogen-bonded motifs occur, each involving the hydrogen bond SD(-SO₂-N-H)…O=C(PCL) and the hydrogen bond PCL(O-H)…N(SD pyrimidinyl). A significant inequality of the two N…O distances in the chemically identical N-H…O=C hydrogen bonds indicates that such parameters can be strongly influenced by the crystal packing factors.