To clarify whether and how PTEN and the phosphatidylinositol 3-kinase/Akt pathway relates to endometrial cancer we examined the expression of these pathway-related proteins in patients with endometrial cancer. Of 103 endometrial cancers, 37 (36%) showed negative immunohistochemical staining for PTEN. Western blotting revealed that the level of phosphorylated Akt expression in PTEN-negative cases was significantly higher compared with that in positive cases. We found a significant inverse correlation between PTEN and phosphorylated Akt. The present study indicates the phosphorylation of Akt accompanied by the loss of PTEN in clinical specimens of endometrial cancers. In order to investigate the relationship between PTEN expression and prognosis in endometrial cancer, 98 patients with advanced endometrial cancer were newly enrolled. The survival rate for PTEN-positive patients was significantly higher than that for PTEN-negative or -heterogeneous staining patients. Of the 98 patients, 25 underwent radiation therapy, 62 received chemotherapy after surgery, and the remaining 11 did not have any postoperative treatment. When patients underwent chemotherapy, the survival rate for PTEN-positive cases was clearly higher than that for PTEN-negative or -heterogeneous cases (62.4 vs 11.8%). Subsequent multivariate analysis revealed that PTEN staining was an independent prognostic factor for patients undergoing chemotherapy. The current study demonstrates that PTEN-positive staining is a significant prognostic indicator of favorable survival for patients with advanced endometrial cancer who undergo postoperative chemotherapy.