Dermoid cysts, which are lined by ectoderm elements, typically arise in skin, testicles, and ovaries. These cysts mostly occur during the second or third decade of life and rarely present in children. We describe a rare case of a dermoid cyst in a 6-year-old Japanese girl. Examination showed a smooth, well-defined cystic swelling approximately 30 × 20 mm 2 in the midline of the oral floor. The cyst was excised via the intraoral approach under general anesthesia. The histopathologic diagnosis of a dermoid cyst was made. The clinical outcome was satisfactory without postoperative complications during the 26-month follow-up period. K E Y W O R D S child, dermoid cyst, oral floor | 115 MIYAMOTO eT Al.