Background: Unplanned presentations and admissions to hospital among outpatients with cancer are a key indicator of quality care in cancer services. Nutritional issues including malnutrition and dehydration, which fall under the dietitian's scope of practice, can result in unplanned contacts. The present review focused on cancer outpatients undergoing radiotherapy as a particular at risk group and aimed to provide a comprehensive overview of the range and prevalence of nutrition-related unplanned contacts and the associated factors, including the role of dietetic intervention. Methods: A systematic review analysed studies published between 1990 and August 2016 from five databases. Eligible studies reported rates of nutrition-related unplanned contacts among adult nonhaematological cancer outpatients, treated with nonpalliative radiotherapy. Studies were screened for eligibility, extracted, descriptively analysed and synthesised. Results: Fifteen studies were included. Common causes of nutrition-related unplanned contacts included dehydration and enteral feeding commencement and complications. Factors that influenced nutrition-related unplanned contacts included tumour location and stage, treatment modality and the presence of a feeding tube. There were issues in determining the prevalence and identifying dietetic interventions partly as a result of the heterogeneity in reported study designs and varying definitions of nutrition-related unplanned contacts. Conclusions: Nutrition-related problems appear to be associated with unplanned contacts in cancer outpatients undergoing radiotherapy. Hence, there is a strategic need for dietetic involvement aiming to reduce these. Further research is required to define the role of the dietitian in managing nutrition-related unplanned contacts, particularly for dehydration. This may help to define the full scope of practice for dietitians caring for these nutritionally vulnerable and complex outpatients.