The title acid, C10H12O2S, crystallized in the centrosymmetric space group P2(1)/c with one molecule in the asymmetric unit. There is a single hydrogen bond, in which the O and H atoms are ordered and OD...OA is 2.658(2) A. The hydrogen bond forms a cyclic dimer, with graph-set descriptor R2(2)(8), about a center of symmetry. The dihedral angle between the best-fit planes of the benzene ring and the carboxyl group is 13.6(1) degrees.