The acid-catalyzed hydrolysis of dimethyl ether (DME) to methanol was examined using ab initio density functional metadynamics simulations. Diffusion of the acid proton from the aqueous medium, leading to the formation of a protonated DME, is 12.3 kcal mol(-1) activated and 9.3 kcal mol(-1) endothermic, indicating a greater affinity of the acid proton to water than to the ether group. Subsequent scission of the protonated ether bond is found to be 30.7 kcal mol(-1) activated, leading to the formation of a solvated methyl-carbocation, which is thermodynamically unstable. The methyl-carbocation reacts readily to form methanol and regenerate the acid proton.