4,6-Dimeth-oxy-2-(methyl-sulfan-yl)pyrimidine-4-hy-droxy-benzoic acid (1/1).

The base mol-ecule of the title co-crystal, C7H10N2O2S·C7H6O3, is essentially planar, with a maximum deviation of 0.0806 (14) Å for all non-H atoms. The acid mol-ecule is also nearly planar, with a dihedral angle of 8.12 (14)° between the benzene ring and the carb-oxy group. In the crystal, the acid mol-ecules form an inversion dimer through a pair of O-H⋯O hydrogen bonds with an R2(2)(8) ring motif. The pyrimidine mol-ecules are linked on both sides of the dimer into a heterotetra-mer via O-H⋯N and C-H⋯O hydrogen bonds with R2(2)(8) ring motifs. The heterotetra-mers are further linked by weak C-H⋯O hydrogen bonds, forming a tape structure along [1-10].