Tumorigenic activity of cyclooxygenase-2 (COX-2), a rate-limiting enzyme in the production of prostaglandins (PGs), has been proved for some types of cancer, including brain tumors. We evaluated expression of COX-2 in meningioma, one of the most common intracranial tumors in adults which accounts for 24-30 % of intracranial tumors. We performed immunostaining for COX-2 in 76 cases of meningioma consisting of 44 cases of low-grade (WHO Grade I) and 32 cases of high-grade (29 cases of Grade II and 3 cases of Grade III) meningioma, and evaluated COX-2 expression levels on the basis of staining intensity and proportion in tumor cells. The expression level of COX-2 in meningioma cells was significantly correlated with WHO grade (P = 0.0153). In addition, COX-2 expression was significantly correlated with MIB-1 labeling index for all 76 cases of meningioma (P = 0.0075), suggesting tumor promotion by COX-2 in meningioma progression. Our results may indicate the therapeutic value of non-steroidal anti-inflammatory drugs against meningioma, especially for patients with elevated proliferation, to regulate the tumorigenic activity of COX-2 in meningioma cells.