The sense of balance relies on vestibular hair cells, which detect head motions. Mammals have two types of vestibular hair cell, I and II, with unique morphological, molecular, and physiological properties. Furthermore, each hair cell type signals to a unique form of afferent nerve terminal. Little is known about the mechanisms in mature animals that maintain the specific features of each hair cell type or its postsynaptic innervation. We found that deletion of the transcription factor Sox2 from Type II hair cells in adult mice of both sexes caused many cells in utricles to acquire features unique to Type I hair cells and to lose Type II-specific features. This cellular transdifferentiation, which included changes in nuclear size, chromatin condensation, soma and stereocilium morphology, and marker expression, resulted in a significantly higher proportion of Type I-like hair cells in all epithelial zones. Furthermore, Sox2 deletion from Type II hair cells triggered non-cell autonomous changes in vestibular...