Genetic and immunohistochemical studies may provide insight into the mechanisms of vestibular schwannoma (VS) recurrence following radiation therapy. Stereotactic radiation therapy is an increasingly common alternative to microsurgical resection for the primary management of sporadic VS. The molecular mechanisms associated with recurrent vestibular schwannoma (VS) following radiation therapy are not known. Primary or irradiated VS tumors were fresh-frozen at the time of surgical resection and microdissected to undergo DNA extraction. Lymphocytic control DNA was isolated from blood obtained by venipuncture. Paired normal and tumor DNA specimens were analyzed for allelic loss by PCR amplification of polymorphic dinucleotide repeat sequences. Immunohistochemical studies were performed on paraffin-embedded, irradiated surgical specimens. Using 16 polymorphic microsatellite markers, 20 of 26 non-irradiated VS demonstrated loss of heterozygosity (LOH) in at least one locus of chromosome 22q. In contrast, none of the four irradiated recurrent VS demonstrated LOH on chromosome 22q (p = 0.008). No allelic loss was seen in either the primary or irradiated VS utilizing markers mapping to chromosome 10. Deletions on chromosome 10 are seen in both benign and higher-grade meningiomas and intracranial malignancies associated with radiotherapy. Immunohistochemical studies were performed to detect the protein product of the NF2 gene, merlin, in the four irradiated VS. NF2 staining was not observed. This study represents the first microsatellite and immunohistochemical analysis of recurrent VS following radiation therapy. Our preliminary observations suggest an alternative mechanism of NF2 inactivation that may correlate with radioresistance in VS.