beta-Catenin, a multifunctional protein related to the adherens junction and to signal transduction, is a key molecule of cell proliferation, and it is central to epithelial architecture, regulating the polarity of cells and tissues. beta-Catenin stabilization may play a key role in epidermal signaling leading to hair development, and its aberrant activation may be implicated in formation of hair tumors. Several investigators have shown that pilomatricomas are frequently associated with beta-catenin mutation. In this study, we confirmed beta-catenin gene (CTNNB1) mutation in human pilomatricomas (100% frequency) from which adequate DNA could be obtained for gene analysis. A novel mutation, D32N, was found in one case of pilomatricoma. A preliminary immunohistological study revealed prominent beta-catenin staining in basophilic cells of pilomatricomas, especially in nuclei. Benign tumors which were considered to be derived from hair matrix or hair follicles, and other benign skin tumors, were also investigated. beta-Catenin mutations were not detected in any of the these tumors. These results seem to indicate that hair matrix cells are key players in hair development. Investigation into gene abnormalities of hair-follicle tumors may elucidate the cause of their neoplastic transformation, and may provide a suggestion for the mechanism of hair development.