Waardenburg syndrome (WS) is associated with neural crest-derived melanocyte deficiency caused by mutations in either one of three transcription factors: MITF, PAX3, and SOX10. However, the hierarchical relationship of these transcription factors is largely unknown. We show that SOX10 is capable of transactivating the MITF promoter 100-fold, and that this transactivation is further stimulated by PAX3. Promoter deletion and mutational analyses indicate that SOX10 can activate MITF expression through binding to a region that is evolutionarily conserved between the mouse and human MITF promoters. A SOX10 mutant that models C-terminal truncations in WS can reduce wild-type SOX10 induction of MITF, suggesting these mutations may act in a dominant-negative fashion. Our data support a model in which the hypopigmentation in WS, of which these factors have been implicated, results from a disruption in function of the central melanocyte transcription factor MITF.