Aggressive fibromatosis [AF] with bone involvement in the head and neck is a rare neoplasm. The clinical and radiological findings are non-specific, the histological diagnosis is often difficult and an inadequate excision will result in recurrence. A four year-old boy was referred to our department with a fast growing painless mass of the mandible. Excision biopsy revealed AF. Local excision of the tumor was performed but six months after surgery a rapid recurrence was detected. The tumor was unresectable and the boy was treated with a low-dose chemotherapy including methotrexate and vinblastine for one year. Completion of surgical excision is planed afterwards. Although AF are only locally aggressive, their treatment is complex. To avoid disharmonious facial growth alternative modes of therapy should be considered in extended AF. Keywords: aggressive Fibromatose, Unterkiefer, Weichteilsarkom, Rezidiv, radikale Tumoroperation