From April 1997 until September 1998 an observational study was performed with respect to the quality of the “informed consent procedure concerning patients who were candidates to participate in the EORTC-trial 10925/22922. This phase-III trial deals with the question of whether irradiation of the internal mammary chain together with the ipsilateral supraclavicular chain leads to a better survival in patients with operable breast cancer. Patients with either medially located primary tumours or with (ipsilateral) axillary lymph node metastases were eligible for participation. Patients were, in our study, considered eligible if they were candidates for participation in the above mentioned EORTC-trial. After they had agreed to participate in the informed consent study, 2 radiological technologists interviewed 51 patients. It appeared that patients were well aware of it) the important characteristics of their disease; ii) the purpose of the treatment; iii) the fact that they were candidates for participation in a phase-III trial; iv) the fact that randomisation had taken place (for the participants). According to the answers of the patients it appeared that the quality of the information, as given by their physician, was good. Further attention needs to be given to the time allocated to the patients to consider their participation in the trial. The quality of the informed consent procedure could be measured adequately. Preferably this type of analysis should be performed at the start of a (large) trial. By doing so, the quality of the informed consent procedure can be evaluated and eventually the quality of the procedure can be improved.