Meningiomas are the most commonly reported brain tumor in the United States. Though these tumors are often surgically curable, even World Health Organization (WHO) grade 1 meningiomas can recur. The variability seen in the clinical behavior of meningiomas suggests that these tumors are genetically heterogeneous. The most common genetic aberrations found in meningiomas are deletions of chromosomes 1p, 14q, and 22q. Fluorescent in situ hybridization (FISH) analyses have demonstrated the presence of intratumor heterogeneity; however, the loss of a single chromosome region was not indicative of aggressive behavior. In fact, tumors of higher grade are less heterogeneous in that all of the cells tend to demonstrate deletion of these chromosome arms. Tumor suppressor genes that map to these chromosomes have been identified but have not been found to play a significant role in the initiation or progression of the disease. The identification of a marker of aggressive behavior would allow the development of improved clinical protocols based on early intervention for those patients likely to experience a recurrence.