Odontomas are developmental malformations of dental tissues, and they may interfere with the eruption of the associated tooth. Odontomas have limited growth potential, and their occurrence in the primary dentition is uncommon. This article describes a case of a large complex odontoma in a 5.2-year-old boy that prevented eruption of the mandibular left lateral incisor. The odontoma was surgically removed, routine follow-up was done for more than a year, and no recurrence was seen. Palabras clave: anterior mandible, complex odontoma, mixed tumor, odontogenic tumor, opaque lesion, primary tooth