Background and purpose: To report recommendations given in the Multinational Association of Supportive Care in Cancer (MASCC) International Consensus Conference regarding the use of antiemetics in radiotherapy. Patients and methods: A steering committee under MASCC auspice chose panel participants for the guidelines development process on prevention of chemotherapy- and radiotherapy-induced emesis (RIE). Pertinent information from published literature as of March 2004 was reviewed for the guideline process. Both the MASCC level of scientific confidence and level of consensus, and the American Society of Clinical Oncology (ASCO) type of evidence and grade for recommendation were adopted. Results: Total body irradiation is classified at high risk, upper abdomen at moderate, lower thorax, pelvis, cranium (radiosurgery) and craniospinal at low, head and neck, extremities, cranium and breast at minimal risk. The recommendations for the use of antiemetics in radiotherapy are as follows: prophylaxis with a 5-HT3 antagonist in patients at high and moderate risk levels of RIE (±dexamethasone in the former group), prophylaxis or rescue with a 5-HT3 antagonist in the low risk group, and rescue with dopamine or a 5-HT3 receptor antagonist in minimal risk level. Conclusions: These recommendations represent a valid tool for prophylaxis and treatment of RIE in clinical practice. © 2005 Elsevier Ireland Ltd. All rights reserved.