Objective: To evaluate the scored Patient-generated Subjective Global Assessment (PG-SGA) tool as an outcome measure in clinical nutrition practice and determine its association with quality of life (QoL). Design: A prospective 4 week study assessing the nutritional status and QoL of ambulatory patients receiving radiation therapy to the head, neck, rectal or abdominal area. Setting: Australian radiation oncology facilities. Subjects: Sixty cancer patients aged 24-85 y. Intervention: Scored PG-SGA questionnaire, subjective global assessment (SGA), QoL (EORTC QLQ-C30 version 3). Results: According to SGA, 65.0% (39) of subjects were well-nourished, 28.3% (17) moderately or suspected of being malnourished and 6.7% (4) severely malnourished. PG-SGA score and global QoL were correlated (r = - 0.66, P < 0.001) at baseline. There was a decrease in nutritional status according to PG-SGA score (P < 0.001) and SGA (P < 0.001); and a decrease in global QoL (P < 0.001) after 4 weeks of radiotherapy. There was a linear trend for change in PG-SGA score (P < 0.001) and change in global QoL (P = 0.003) between those patients who improved (5%) maintained (56.7%) or deteriorated (33.3%) in nutritional status according to SGA. There was a correlation between change in PG-SGA score and change in QoL after 4 weeks of radiotherapy (r = -0.55, P < 0.001). Regression analysis determined that 26% of the variation of change in QoL was explained by change in PG-SGA (P = 0.001). Conclusion: The scored PG-SGA is a nutrition assessment tool that identifies malnutrition in ambulatory oncology patients receiving radiotherapy and can be used to predict the magnitude of change in QoL.