Hundred forty-four correlations are reported between radiological simulation and CT-scan in cases of prostate adenocarcinoma without metastases treated from 1980 to 1986 exclusively by transcutaneous radiotherapy using the box technique with 25 MV photons. Forty-eight percent of the cases were intracapsular forms. On the basis of correlation criteria defined, the prostatic boost volume was shifted in the sagittal plan in 18% of the cases. Suspect seminal vesicles were found in 60% of the cases. Our treatment plans were considered "correct" in 65% of the cases, "acceptable" in 26% of the cases and "unsatisfactory" in 29% of the cases. The corrections applied to the treatment plan do not vary according to grade but according to stage and concern mainly the posterior limit of the boost volume and to a lesser extent the superior and anterior limits. The boost volume should be determined specifically for each case. CT-scans thus seem indispensable in establishing treatment plans in prostate cancer.