Meningiomas are usually benign tumors; however, they can recur after surgical resection and occasionally show histologic progression to a higher grade II and III malignancy. The second most frequently reported genetic abnormality after 22q loss is deletion of 1p, although alterations in 9q, 10q, and 14q are also implicated in meningioma progression. Fourteen tumors comprising six benign, four atypical, and four malignant meningiomas were examined by means of cytogenetic and fluorescence in situ hybridization analysis. All tumors showed losses in different regions of 1p, with 1p11, 1p13, 1p21, 1p22, 1p32, and 1q21 breakpoints; eight tumors also presented alterations of chromosome 14. Five of the six cases with deletions on 1p and normal chromosome 14 were grade I, and two were recurrent. All but one of the eight cases with simultaneous 1p deletion and alterations of chromosome 14 were grade II (3 cases) and grade III (4 cases); all the grade III cases were recurrent. These results support the possible association between changes in 1p and chromosome 14 with the evolution of aggressive meningiomas through tumor progression.