While mutations in Sox4, a member of the SRY-like HMG box gene family, have been associated with a variety of human disorders and embryonic defects in the mouse, the structure and developmental expression of Sox4 in the avian embryo has not been described. We have isolated and characterized the chicken Sox4 gene. The chicken Sox4 gene shows a high degree of sequence homology with the mouse and human Sox4 genes, particularly in the HMG-like DNA binding domain and at the carboxy terminus. Furthermore, our in situ hybridization studies document an expression pattern during embryonic development that is very similar to that described for the mouse, particularly with regards to expression in the developing heart. However, abundant expression was also detected in tissues of neural crest origin including pharyngeal arch and craniofacial mesoderm, supporting a potential primary role in neural crest cardiac pathology previously detected in Sox4 mutant mice. Furthermore, a reciprocal pattern of Sox4 and Sox11 expression in the developing neural tube was detected in the chicken compared to that seen in the mouse. These studies suggest that Sox4 plays an important and conserved role in the embryonic development of these structures in the chicken as well as in the mouse and lay the foundation for future studies of the role of Sox4 during critical events of organogenesis.