An electron microscopic study of the intraoral lesions of Darier's disease demonstrated a defect of desmosomes and tonofilaments in the early development of affected mucosa. Marked cytoplasmic vacuolation, keratohyaline granule formation and nuclear pyknosis as reported in skin acantholytic cell ultrastructure was not conspicuous in the oral mucosa of the case reported. The clinical diagnosis, histopathologic diagnosis, pedigree and treatment of Darier's disease is discussed.