Meningiomas are common central nervous system tumours which present usually in the 4th and 5th decades of life. Loss of constitutional heterozygosity on chromosome 22 in 60% of sporadic meningiomas has implied the involvement of a tumour suppressor gene. The neurofibromatosis type 2 gene (NF2), a prime candidate for involvement in meningioma, was screened for point mutations. After examining eight of the 16 known NF2 exons in 151 meningiomas, 24 inactivating mutations were characterized. Significantly, these aberrations were exclusively detected in tumours which lost the other chromosome 22 allele. These results provide strong evidence that the suppressor gene on chromosome 22, frequently inactivated in meningioma, is the NF2 gene, and suggest that another gene is involved in the development of 40% of meningiomas.