The aim of this study was to compare the effectiveness of Calendula officinalis with that of trolamine, which is considered in many institutions to be the reference topical agent for acute dermatitis after radiotherapy. Between July 1999 and June 2001, 254 patients who had been operated on for breast cancer and who were to receive postoperative radiation therapy were randomly allocated to application of either trolamine (128 patients) or C. officinalis (126 patients) on the irradiated fields after each session. The primary endpoint was the occurrence of acute dermatitis of grade 2 or higher. Secondary endpoints were the occurrence of pain, the quantity of topical agent used and patient satisfaction. The occurrence of acute dermatitis of grade 2 or higher was significantly lower (41 vs. 63%) with the use of C. officinalis than with trolamine. Moreover, patients receiving C. officinalis had less frequent interruption of radiotherapy and significantly reduced radiation-induced pain.