Applied TNM-system for determination and prognostic classification of the cancer patients of Oral and Maxillofacial region does, however, only partly justice, if at all, to the nature of the tumor disease. And the TNM-system implies among other defects a crude simplification of the complex pattern of the tumor disease. But in clinical practice, the prognosis must be determined on the bases of a specific combination of clinical factors under consideration of various therapeutical conditions. For more reliable and objective prognosis determination for the cancer patients of Oral and Maxillofacial region, `Retrospective DOSAK(German-Austrian-Swiss Association for Head and Neck Tumors) study' introduced Treatment-dependent Prognosis Index TPI in 1982. Treatment-dependent Prognosis Index TPI gives the clinician an opportunity to determine the prognosis before starting therapy at the time of the first admission of the patient, during the therapy and immediately after complete of the therapy. The fundamental purpose of the TPI can be summarized as follows. 1) In clinical-therapeutical cancer research the TPI provides a sound basis for the planning and verification of therapy studies. 2) In clinical practice the TPI allows a reliable and objective determination of the prognosis for the individual patient and thus provides the clinician valuable assistance in planning the treatment. The authors estimated the survival curves of the 179 cases of squamous cell carcinoma from 1985.1.1 to 1992.8.31 in the Department of Oral and Maxillofacial Surgery, Seoul National University Hospital according to Treatment-dependent Prognosis Index TPI of Retrospective DOSAK study and compared with the survival curves observed in long term study on prognosis of patients.