Six patients with advanced oral squamous cell carcinoma were treated with preoperative concurrent chemoradiotherapy. Chemotherapy consisting of CDDP(60 to 70 mg/m(2), day 1)and 5-FU(600 to 700 mg/m(2), day 1 to 5)with concurrent radiotherapy was accelerated hyperfractionation to target volume of 43-63 Gy. The clinical effect of this therapy on the primary tumor and cervical lymph node was examined in patients who visited our university hospital from 1994 to 2004. The five untreated and one recurrence patients were 3 males and 3 females. Their ages ranged from 23 to 76 years. The primary sites were the tongue in 3, lower gingiva in 2, and upper gingiva in 1 patient(s). Five cases were in advanced Stage IVA and 1 case in Stage III. The preoperative clinical responses of primary tumor: 1 case showed a complete response(CR). The response rate was 100%. We did not operate the case because of CR. Histological effect of the primary tumor(according to the grading system of Ohboshi and Shimosato): 2 patients were CR. Pathological CR rate of primary site was 33%. However, the CR rate of the metastatic lymph nodes was 0%. In terms of adverse effects, all cases developed nausea, mucositis and leucopenia. The most severe were leucopenia(Grade III), sepsis and DIC. This combination chemoradiotherapy has been proven to be very histologically effective for the primary tumor.