Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by development of bilateral acoustic neurinomas and increased incidence of meningiomas. Frequent losses of I allele of chromosome 22 in neurinomas and meningiomas has indicated that the gene responsible for NF2 functions as a tumor suppressor. Although the NF2 gene has been mapped within a 13 cM region between D22S1 and D22S28 by linkage analysis, its location with respect to D22S15 is uncertain. We previously reported an NF2 patient with a constitutional balanced translocation t(4;22)(q12;q12.2); the NF2 gene is probably disrupted at the breakpoint. To define the location of this breakpoint on chromosome 22, we performed fluorescence in situ hybridization (FISH) with DNA markers in the NF2 region and determined the physical order of 5 loci: D22S1-NF2-LIF-D22S15-D22S32.