Phosphatase and tensin homolog (PTEN), a negative regulator of the phosphatidylinositol 3-kinase/Akt pathway, is one of the most frequently mutated/deleted tumor suppressor genes in human cancers. The aim of this study was to gain insight into the role played by PTEN in intestinal homeostasis and epithelial cell function. Using the Cre/loxP system, we have generated a mouse with a conditional intestinal epithelial Pten deficiency. Pten mutant mice and controls were sacrificed for histology, immunofluorescence, Western blot, and quantitative polymerase chain reaction analysis. Our results show that loss of epithelial Pten leads to an intestinalomegaly associated with an increase in epithelial cell proliferation. Histological analysis demonstrated significant perturbation of the crypt-villus architecture, a marked increase in goblet cells and a decrease in enteroendocrine cells, suggesting a role for Pten in the commitment of the multipotential-secretory precursor cell. Loss of epithelial Pten does not result in induction of nuclear beta-catenin protein levels, nor is it sufficient to promote tumorigenesis initiation. However, it severely enhances intestinal tumor load in Apc(Min/+) mice, in which c-Myc is already deregulated. These results reveal an unknown function for Pten signaling in the commitment of multipotential-secretory progenitor cells and suggest that epithelial Pten functions as a modifier gene in intestinal neoplasia.