We reviewed 79 patients with squamous cell carcinoma of the lateral wall of the oropharynx who received treatment at the Cancer Institute Hospital, Tokyo, between 1971 and 1990. There were 67 men and 12 women, aged 31 to 81 years (average 59.2 years). The tumors could be staged by TNM classification (UICC 1987) as follows: Stage I 0, Stage II 12, Stage III 27, Stage IV 40. It must be noted that more than 50% of the tumors were classified as stage IV. As the initial treatment, 50 patients underwent radical radiotherapy, and the remaining 29 were treated mainly by surgery after pre-operative radiation. Some patients underwent adjuvant chemotherapy, but the role of chemotherapy was not considered in this study. The purpose of the present study was to derermine the prognostic factors and to determine the survival rate after each treatment modality. The results were as follows: i) Patients with either T4, over N2b or a stage IV tumor had a significantly poor prognosis. ii) Cox multivariate analysis revealed that age, local extension (base of tongue, anterior pillar, soft palate and mid-line), pathological findings (poorly, moderately or well differentiated), tumor type (exophytic or endophytic) were not useful prognostic factors. iii) Radiosensitivity was not reflected in the survival rate judging from the high recurrence rate (44%) after radical radiotherapy. On the other hand, local recurrence after radical resection was seen in 18% of the patients. iv) Analysis of the data supported the recommendation of surgery after preoperative radiation as the treatment for stage III patients. It seems difficult to find the best treatment modality for stage IV patients in order to improve the survival rate, and this is an issue that still remains to be resolved. v) From the study of the surgical specimens, we are unable to demonstrate a significant survival advantage of the patients with a high grade radiation effect, or patients with no vessel involvement.