Osteosarcoma is an infrequent, locally aggressive neoplasm in the head and neck region. To date, surgery is the mainstay of treatment. However, patients with mandibular osteosarcomas usually have a locally advanced disease at diagnosis and therefore represent a therapeutic challenge because surgical margins are difficult to obtain due to aesthetic and functional concerns. To evaluate possible prognostic factors implicated in recurrence, persistence or relapse in osteosarcoma of the mandible, with special reference to the soft tissue and bone surgical margins. A series of 20 patients with mandibular osteosarcomas treated at the Instituto Nacional de Cancerología (México) from 1985 to 1999 are reviewed. There were 14 female and 6 male patients. Twelve cases were treated with surgery alone, 3 patients with surgery and adjuvant radiotherapy, 1 had neoadjuvant chemotherapy followed by surgery, 1 had neoadjuvant chemotherapy, surgery and postoperative radiotherapy, 1 with surgery and adjuvant chemotherapy, 1 with surgery followed by adjuvant chemotherapy and radiotherapy and one patient rejected treatment. Between 1985 and 1992 these neoplasms were treated by means of total mandibulectomy, independently of tumor size, but between 1993 and 1999 the policy was to practice smaller resections but long enough to obtain macroscopic surgical free margins. In the first period the relationship between mandibular size resection and tumor size was 1.9, meanwhile in the second period the relation was 1.5. There was not significant difference between both periods in terms of tumor size (6.0 cm vs. 6.02 cm at the time of surgery) nor in local control and survival. Soft tissue involvement as reported by histological study was strongly associated with recurrence (p = 0.0024). Overall 5-year survival was 20%. A policy of total mandibulectomy is not associated with a better local control or survival. Extent of resection must be tailored with tumor size. Extent of margins in soft tissue is the limiting factor for local control.