Metaplasia, in general, and intestinal metaplasia, in particular, are transdifferentiation processes triggered by environmental aggressions. The heterogeneity of different morphologic variants of metaplasia and distinction from close morphologic entities--heterotopia and hamartoma--is reviewed. Recent data on the characterization of the molecular and epidemiological data involved in the development and progression of lesions of gastric intestinal metaplasia are discussed. A redefinition of intestinal metaplasia is proposed.