Desmoplastic fibroma (DF) is a very rare bone tumor, classified as a benign lesion. It might be locally a very aggressive tumor with a high rate of recurrence after surgical resection. We present a case of a 3-year and 6 month-old patient, with mandibular desmoplastic fibroma. The clinical, imaging, histological findings and surgical treatment are discussed and, also, a brief review of the literature of DF is presented. The purpose of this case report is to emphasize the particularity of the case, ultrasound findings and the main differential diagnostic of this rare bone tumor.