Complex odontoma is a histologically differentiated tumorous lesion consisting mainly of dentine and enamel. Its histological structure is complex and diverse. Recently, we encountered a complex odontoma which showed an extremely rare histological structure. The tumor consisted mainly of cementum and was hollow and did not contain hard tissue. We performed histological studies by microradiography and report the results here.<BR>The patient was a 29-year-old male. He presented with an abnormality of the right mandibular ramus on radiographic examination. The abnormality was diagnosed to be a benign tumor. The tumor was removed under general anesthesia.<BR>The tumor was calcified, had a lamellar structure, was hollow. Dentine and enamel were observed interspersed with cementum, which was the main component of the tumor.