A mild and efficient organic solvent free process has been developed for the synthesis of 4-(4-hydroxyphenyl)butanoic acid, a key intermediate in the synthesis of LY518674. Thus we have achieved the demethylation of 4-(4-methoxyphenyl)butanoic acid with only a slight excess of aqueous HBr and without phase transfer catalysis. In addition, 4-(4-hydroxyphenyl)butanoic acid is easily obtained by direct crystallization from the reaction mixture.