Résumé : To improve surgical results of potentially operable rectal cancer (T2, T3, T4, Mo), the European Organization for Research on Treatment of Cancer (EORTC) conducted a two-arm randomized clinical trial to evaluate the effect of administering radiotherapy before radical surgery. Four hundred ten patients were allocated to be treated either by surgery alone or by 34.5 Gy of radiotherapy (in 19 days overall) followed by surgery. The tolerance of the adjuvant radiation therapy was fairly good. The 5-year survival rate was 65% overall and showed no difference between both therapeutic regimens. Similarly, the metastases-free rate was the same in both groups. In contrast, the preoperative radiation therapy showed a marked effect on local control of the disease, the comparison of the time to local recurrence being highly significant between the two treatment groups (P = 0.001). The proportion of patients free of local recurrence at 5 years was 85% in the combined treatment versus 65% in the group of patients treated by surgery alone.