Our knowledge of meningioma has expanded considerably in the last few years. Immunohistochemistry, cytogenetics and molecular biology have given an important contribution to this improvement. Meningiomas can have almost endless variations in cellular morphology, architectural patterns and metaplastic changes. The majority of them have no prognostic implications. But a few variants should be recognised because of peculiar clinico-pathologic correlations or biological behavior. Histological features useful in distinguishing benign from potentially aggressive meningiomas have been identified. According to the WHO classification meningiomas are classified as benign (Grade 1), atypical (Grade 2) and anaplastic (Grade 3). Since histological appearance fails to predict accurately the clinical behaviour in a significant percentage of meningiomas, the attention has turned from tumor histology to tumor biology. Proliferative indices can be used, together with other histologic features, in assessing the prognosis as well as the postoperative management of the patients. Karyotyping may be of use to identify a subgroup of patients at higher risk for recurrence who may need special follow-up and treatment. The most consistent chromosome aberration in meningiomas seems to be a monosomy 22. As the karyotype becomes progressively abnormal, the tumor becomes more aggressive. Molecular genetic analysis has shown that TP53 gene mutation may be considered as a marker for malignant transformation in meningioma. P53 immunoreactivity is not always associated with the gene mutation but is not detectable in benign meningiomas.