This retrospective study involved 150 patients treated for oropharyngeal carcinoma by external radiotherapy alone at the Institut Gustave-Roussy. The midplane tumor dose was 70 Gy delivered in 7 weeks. During 1981, 63 patients were treated with 5 fractions (5 F) of 2 Gy per week. The following year, 87 patients, were treated with 4 fractions (4 F) of 2.5 Gy per week. Prognostic factors were equally distributed in both groups. The locoregional tumor control was 83% for the 4 F patients and 83% for the 5 F patients. Degree and incidence of acute reactions with both fractionation regimens were similar. Necrosis of the oropharyngeal mucosa and trismus were significantly more severe and more frequent in the 4 F group (23% and 20% respectively) than in the 5 F group (10% and 5% respectively) (p = 0.03 and p = 0.01). Other late effects such as skin necrosis (6% in the 4 F group versus 0% in the 5 F group) and severe cervical sclerosis (12 vs 5%) were also more frequent in the 4 F group than in the 5 F group but the difference was not significant. The results suggest a greater sensitivity of late compared to early normal tissue effects and of tumor response to an increase in dose per fraction (from 2 Gy to 2.5 Gy) in oropharyngeal carcinoma.