The title compound, C(10)H(13)N(3)O(2)S, was prepared by condensation of 3,4-dihydroxy-benzaldehyde with 4-ethyl-3-thio-semicarbazide. The mol-ecule adopts an E configuration with respect to the C=N bond. One of the OH substituents on the dihydroxy-benzene ring is disordered over the two possible 3-positions on either side of the ordered 4-hydr-oxy group. The occupancy of the major disorder component refined to 0.633 (7). The mol-ecule is essentially planar, with an r.m.s. deviation through all non-H atoms of 0.0862 Å. An intra-molecular N-H⋯N hydrogen bond forms between the outer amine residue and the imine N atom, generating an S(5) ring motif and contributing to the planarity of the mol-ecule. In the crystal structure, an extensive network of classical O-H⋯O, O-H⋯S and N-H⋯S hydrogen bonds and weak C-H⋯O and S⋯O [3.301 (3) Å] inter-actions link mol-ecules into sheets running approximately parallel to the ab plane.