A six-year-old girl is presented with an increasing mass involving the anterior vestibule and the floor of the mouth. Histologic and immunohistochemical examination revealed a poorly differentiated epitheloid leiomyosarcoma with destruction of the mandible. According to the CWS-96-study the patient underwent preoperative chemotherapy followed by complete resection of the mandibular body with the surrounding soft tissues. Recurrent tumor became evident only three months later on. The further treatment consisted of tumor resection, oral chemotherapy and irradiation. Nevertheless tumor control could not be achieved. The patient died of progressive disease 16 months after diagnosis. Leiomyosarcoma is extremely uncommon in childhood, especially with localisation in the oral cavity. Diagnosis is based on histologic examination and immunohistochemistry. In the presented case the lack of smooth muscle actin expression made diagnosis difficult. The preoperative chemotherapy could not achieve reduction of tumor size, so that extensive surgery became necessary. Estimation of the prognosis of the oral leiomyosarcomas in childhood is difficult. High grade tumours and involvement of bone seem to be associated with bad clinical outcome. The presented case is confirming that.