Conventional two-dimensional (2-d) treatment planning was compared to three-dimensional (3-d) treatment planning for patients with prostatic carcinoma. Both types of treatment planning were performed for all ten patients with five fixed fields. In 3-d planning we used irregular shaped fields. For further evaluation we performed conventional planning in rotation technique in two patients. The target volume included prostate, seminal vesicles and a surrounding security margin of 2 cm. Using the MPR-version of the MEVAPLAN planning system, the three-dimensional dose calculations were performed. For the volumes of interest (VOI's) we discussed quality of the dose distribution concerning homogeneity in the target volume and isodose distribution in the organs at risk, which are the rectum and the urinary bladder. We defined the tumor encompassing reference isodose (ca. 95%) for the calculation of the involved rectum- and bladder volume. Using the five-field technique our results show a reduction of the radiation related rectum- and bladder volume concerning the tumor encompassing reference isodose (ca. 95%) for the rectum in between 9.5 and 36.6% (median: 19%, n = 10) and for the urinary bladder in between 15.7 and 47.8% (median: 28%, n = 10). Calculated for 80% of the reference isodose the difference for the rectum was 15.7 to 31.3% (median: 23%) and for the urinary bladder 24.5 to 56.7% (median: 42%). A significant reduction of radiation related side-effects concerning rectum and urinary bladder can be expected by a reduction of volume involvement and a consecutive dosage limitation.