The water-assisted hydrolysis of formamide has been studied at the MP3/6-31G**//3-21G ab initio level for neutral and H3O+-promoted processes. The computations predict an important catalytic effect through O-protonation, in agreement with previous results for the nonassisted reaction. Assistance by a water molecule lowers the free energy barriers of the neutral and the acid-promoted reactions, but the effect is especially large in the second case. The influence of electrostatic interactions with the bulk is discussed using a continuum model to represent the liquid. Substantial modifications of the transition-state geometries are predicted, but the average change in the activation barriers is rather small.