In xanthene-9-carboxylic acid, C14H10O3, hydrogen bonding is of the cyclic dimer type but involves two crystallographically inequivalent molecules and does not occur about a center of symmetry. The carboxylic H atoms are ordered. The dihedral angle (fold angle) of the xanthene core is 14.2 (1) degree for molecule A and 11.3 (2) degrees for molecule B. The planes of the carboxyl groups are almost perpendicular to the xanthene cores.