Atypical meningiomas are defined according WHO criteria as tumours characterized by: increased mitotic activity or three or more of the following histologic features: increased cellularity, small cells with a high nuclear/cytoplasmic ratio, prominent nucleoli, patternless or sheet like growth, and foci of “spontaneous” or “geographic” necrosis. It means, that those meningiomas which reveal only one or even two from above mentioned features are, according to WHO classification, still consistent with diagnosis of benign (GI WHO) tumours. Histologic slices from 65 atypical meningiomas were investigated and presence of each from those diagnostic histologic criteria which were mentioned above, were taken to account. Additionally, in the same way 59 benign meningiomas, which showed one or two histologic features characteristic for atypical type of the tumours, were analysed. In all cases immunohistochemical reaction with MIB-1 antibody was carried out and proliferating indices (PI) were established using image analysis computer system. Correlation between histologic criteria for atypical meningiomas and proliferating indices of the tumours was statistically estimated. We found a significant relationship between PI and mitotic activity, necrosis, small cells changes, patternless growth, nucleolies and number of histologic features that tumors present.