The chromosomal 1p/19q state was analyzed in 16 low-grade meningiomas and 7 atypical meningiomas using fluorescent in situ hybridization (FISH) analysis. Chromosome 1p aberrations were observed in all atypical meningiomas, but in only one low-grade meningioma. Atypical meningiomas showed 19q deletion or imbalance, suggesting chromosomal instability of 19q. A small group of low-grade meningioma showed 19q aberrations. FISH 1p/19q deletion/imbalance analysis is a sensitive method for detecting chromosome aberrations of meningiomas and provides useful information for grading of meningiomas. Patients with low-grade meningioma with chromosomal instability of 1p/19q should be followed up carefully. Assessment of the chromosomal state by FISH might be of crucial importance in the clinical management of meningiomas.