OBJECTIVE: PTEN is a novel tumor-suppressor gene located on chromosomal band 10q23. Loss of PTEN function has been implicated in the progression of several types of cancer, including glial tumors. This study is performed to evaluate the difference of PTEN expression between the low grade glial tumors and the high grade one. METHODS: Formalin fixed and paraffin embedded tissues from 15 patients with low grade astrocytoma and oligodendroglioma, and 26 patients with glioblastoma, anaplastic astrocytoma, anaplastic oligodendroglioma and malignant mixed glial tumor were evaluated for PTEN expression by immunohistochemical method. RESULTS: Eleven(73%) of 15 cases of low grade glial tumors revealed PTEN expression and eight(31%) of 26 cases of high grade glial tumors, including glioblastoma, revealed PTEN expression. CONCLUSION: The present study suggests that loss of PTEN expression is related with tumor progression from the low grade glial tumor to glioblastoma.