PTEN is a tumor suppressor gene and its mutation is frequently found in endometrial carcinoma. Recently, the pseudogene of PTEN has been reported to be actively transcribed in a number of cells and tissues and a potential for translation is suggested. For further understanding of the involvement of PTEN in endometrial carcinogenesis, we analysed the expressions of PTEN and the pseudogene in 36 endometrial carcinomas with special reference to the genetic status of PTEN. Mutations of PTEN were found in 42% (15/36) of the endometrial carcinomas. The transcript of the pseudogene was expressed in 6 samples (17%) of 36 endometrial carcinomas, but in none of the normal endometria. Western blot analysis showed no translated protein of the pseudogene in any of the cases. Steady level of PTEN protein expression was observed in all the cases examined. Expression level was consistent among the proliferative endometria, secretory endometria and endometrial carcinomas as long as PTEN protein was not truncated. These results indicate that PTEN is a constitutive protein in the endometrium, so that the somatic mutation of PTEN exerts a crucial effect on the endometrial carcinogenesis. In addition, the presence of the PTEN pseudogene transcript urges us caution for the mutational analysis of PTEN as well as careful choice of the probe for the detection of PTEN transcript.