A case of melanotic neuroectodermal tumor of infancy occurring in the mandible is described. The patient was a 1-month-old boy with a rapidly growing tumor of the mandible. Computed tomography showed 2 well-defined osteolytic lesions in the right mandible. Histopathologic diagnosis of a biopsy specimen was melanotic neuroectodermal tumor of infancy. The tumor was excised with removal of the surrounding bone, but 1(1/2) months later it recurred, and segmental mandibulectomy and reconstruction of the defect with a titanium miniplate was performed. Retrospectively, evidence of recurrence was noted on computed tomography taken on the tenth postoperative day. The recurrence was caused by incomplete removal of the tumor. Histopathologically, the tumor cells of the recurrent lesion were dispersed extensively in the bone marrow, and bone remodeling was active. The surgical procedure may have stimulated tumor cell proliferation and reactive bone formation. The patient was followed for 2 years with no evidence of recurrence or metastasis.