This review summarizes the current knowledge of radiation-induced nausea and vomiting (RINV), which occurs in ap-proximately 50% of patients undergoing radiotherapy. Poor control of the symptoms may result in dehydration and electrolyte disturbances leading to delay or even disruption of the planned schedule, which in turn results in decreased disease control. Patients report RINV as distressing symp-toms, and under-treatment is a major problem. Evidence-based antiemetic guidelines have been developed, but lack of adherence is a barrier to improvement of symptom control and quality of life during radiotherapy.