Cementoblastoma is a rare odontogenic tumor that tends to occur in the jaws of young people. It is most commonly characterized by a circumscribed radiopaque mass attached to the tooth roots and rimmed by a radiolucent zone. To our knowledge, few reports have documented an increase in the size of this tumor. We studied a cementoblastoma arising in the mandibular left first molar of a 13-year-old girl and analyzed the growth of this tumor on computed tomography. During a period of 5 months, the tumor diameter increased by about 4 mm, and the volume increased from 6.484 cm3 to 11.955 cm3.