The invention relates to a novel crystalline form of 3-[[3,5-dibromo-4-[4-hydroxy-3-(1-methylethyl)-phonoxy]-phenyl]-amino]-3-oxopropanoic acid, said crystalline form being characterised by a powder X-ray diffraction pattern having major peaks at 2¸ = 9.0±0.2, 14.7±0.2, 19.6±0.2, 21.6±0.2, and 24.3±0.2.