The crystal structure of 2,4,5-T was determined by the symbolic addition method. 1741 reflections, of which 1326 were considered observed, were collected on a four-circle diffractometer. Crystals are triclinic, Pi, with z = 2, in a cell of dimensions: a 1089.5(6), b 684.8(3), c 683.8(3) pm, a 81.33(4)°, ß 78.90(4)°, ? 83.04(4)°. The structure was refined by least squares to R 0.068. The two molecules are hydrogen-bonded [O...H-O 268.9(7) pm] through their carboxylic acid groups forming a cyclic dimer in a similar manner to 2,4- dichlorophenoxyacetic acid (2,4-D).1 However, the planes of the benzene ring and the carboxyl group are 4.15° away from being coplanar, a fact which is markedly different from that observed in 2,4-D (85.23°) but similar to that observed in the substituted aromatic carboxylic acids. The result of this is a dimer with all atoms except those in the methylene group lying approximately in a plane.