Hirschsprung disease (HSCR, MIM ♯142623) is a multigenic neuocristopathy (neural crest disorder) characterized by absence of enteric ganglia in a variable portion of the distal colon. Subsets of HSCR individuals also present with neural crest-derived melanocyte deficiencies (Hirschsprung-Waardenburg, HSCR-WS, MIM ♯277580). Murine models have been instrumental in the identification and analysis of HSCR disease genes. These include mice with deficiencies of endothelin B receptor (Ednrb^s–l refs 1,2) endothelin 3 (Edn3ls; refs 1,3) the tyrosine kinase receptor cftet4 and glial-derived neurotrophic factor5–7. Another mouse model of HSCR disease, Dom, arose spontaneously at the Jackson Laboratory8. While Dom/+ heterozygous mice display regional deficiencies of neural crest–derived enteric ganglia in the distal colon, Dom/Dom homozygous animals are embryonic lethal8. We have determined that premature termination of SOX10, a member of the SflV–like HMG box family of transcription factors, is responsible for absence of the neural crest derivatives in Dom mice. We demonstrate expression of SOX10 in normal neural crest cells, disrupted expression of both SOX10 and the HSCR disease gene Ednrb in Dom mutant embryos, and loss of neural crest derivatives due to apoptosis. Our studies suggest that SOX10 is essential for proper peripheral nervous system development. We propose SOX10 as a candidate disease gene for individuals with HSCR whose disease does not have an identified genetic origin.