In a previously published insertional mutagenesis screen for candidate brain tumor genes in the mouse using a Moloney mouse leukemia virus encoding platelet-derived growth factor (PDGF)-B, the Sox10 gene was tagged in five independent tumors. The proviral integrations suggest an enhancer effect on Sox10. All Moloney murine leukemia virus/PDGFB tumors had a high protein expression of Sox10 independently of malignant grade or tumor type. To investigate the role of Sox10 in gliomagenesis, we used the RCAS/tv-a mouse model in which the expression of retroviral-encoded genes can be directed to glial progenitor cells (Ntv-a mice). Both Ntv-a transgenic mice, wild-type, and Ntv-a p19Arf null mice were injected with RCAS-SOX10 alone or in combination with RCAS-PDGFB. Infection with RCAS-SOX10 alone did not induce any gliomas. Combined infection of RCAS-SOX10 and RCAS-PDGFB in wild-type Ntv-a mice yielded a tumor frequency of 12%, and in Ntv-a Arf-/- mice the tumor frequency was 30%. This indicates that Sox10 alone is not sufficient to induce gliomagenesis but acts synergistically with PDGFB in glioma development. All induced tumors displayed characteristics of PNET-like structures and oligodendroglioma. The tumors had a strong and widely distributed expression of Sox10 and PDGFR-alpha. We investigated the expression of Sox10 in other human tumors and in a number of gliomas. The Sox10 expression was restricted to gliomas and melanomas. All glioma types expressed Sox10, and tumors of low-grade glioma had a much broader distribution of Sox10 compared with high-grade gliomas.