2-Methyl-sulfonyl-4-(trifluoro-meth-yl)benzoic acid.

In the title mol-ecule, C(9)H(7)F(3)O(4)S, the S and the methyl C atoms of the methyl-sulfonyl group deviate from the benzene ring plane by 0.185 (2) and -1.394 (3) Å, respectively.