The relationship between tumor doubling time, estimated by serial computed tomography (CT), and the proliferating cell nuclear antigen (PCNA) staining index of the tumor specimen was analyzed in 12 patients with nine partially or subtotally resected meningiomas and three meningiomas which recurred after gross total removal. There were nine meningothelial and three fibrous meningiomas. Malignant meningiomas and hemangiopericytomas were excluded. Serial CT was performed at various intervals ranging from 354 to 2007 days. Formalin-fixed, paraffin-embedded archival tissues were immunohistochemically stained using the avidin-biotin complex method with monoclonal antibody against PCNA. Percentages of PCNA-positive cells were calculated in 10 microscopic fields to determine the mean PCNA staining index. PCNA staining indexes varied from 0.13% to 7.46%. The tumor doubling time ranged from 197 to 7943 days and demonstrated a significant inverse rank correlation with the PCNA staining index (r = -0.89, p = 0.003). Meningiomas with PCNA staining indexes higher than 1% have comparatively short tumor doubling times of less than 5 years. PCNA immunostaining is a useful method for evaluating the proliferative activity of meningiomas.