We have determined the structure of 2-(iminocouma-3-yl)-4-(coumar-3-yl)-thiazole, C21H14N2O3S, Mr=372.4, λ = 0.71073 Å, monoclinic, space group P21/n, a = 9.472(2) Å, b = 11.284(2) Å, c = 15.821(3) Å, β = 86.50(2)°, V = 1687.9(6) Å3, Z = 4, Dx = 1.465 Mg m−3, μ(Mo Kα) = 0.207 mm−1, F(000) = 768, S = 1.91, R = 3.82%, wR = 3.26% for 1251 observed reflections (F > 6σF). In the observed conformation of the molecule the imino group forms an intramolecular H…S bond of length 2.26 Å and the carbonyl oxygen makes a short contact with the hydrogen atom of the thiazolyl cycle. The molecule is planar. In the crystal structure a particular disorder of about 20% of molecules is observed with respect to the pseudo-mirror plane which is perpendicular to the molecular plane and passes through the thiazolyl N atom and the middle of the SCH bond. The disagreement found between the observed conformation and that predicted by molecular mechanics calculations is explained by the tendency of the molecule to have the lowest value of dipole moment due to minimisation of the electrostatic contribution to the energy.