PTEN/MMAC1 is a recently characterized tumor suppressor. A pseudogene derived from the human PTEN/MMAC1 phosphatase, psiPTEN, has been reported. Recent analysis of the pseudogene revealed conflicting results about the expression of psiPTEN. In this study, we show that the PTEN/MMAC1 pseudogene is actively transcribed in all cells and tissues examined. In some cases, pseudogene transcripts were found to represent as much as 70% of the total PTEN/MMAC1 RNA. As psiPTEN is transcribed, there is a potential for misinterpretation of PTEN/MMAC1 mutations when RT-PCR techniques are used, as well as potential for a psiPTEN-encoded translation product. Although we were unable to detect a pseudogene protein product in the cell lines examined, a baculovirus produced GST pseudogene fusion protein exhibited phosphatase activity comparable to wild type. The results of this study, taken together, indicate the potential complication of PTEN/MMAC1 molecular analysis caused by the expression of psiPTEN.