Maintaining adequate nutritional status in Head and Neck Cancer (HNC) patients is challenging. Dietetic intervention can improve clinical outcomes. However, many HNC patients are non-compliant with dietary advice when it is provided. Engagement of HNC patients in dietary intervention is complicated by a range of factors including tumour site, radiotherapy side effects and elevated rates of depression and hazardous alcohol use. Behaviour Change Counselling (BCC) is an empirically supported approach for promoting behaviour change. BCC is a collaborative, patient centred approach that incorporates motivational interviewing and behavioural strategies. Assisting dietitians to integrate BCC into standard dietetic consultations represents one mechanism for enhancing compliance with dietetic interventions. Within psychology, positive therapeutic alliance consistently emerges as an important mediator of treatment outcome. The importance of a sound patient-clinician relationship is also beginning to emerge within cancer care. However, little is known about the therapeutic alliance between dietitians and HNC patients. In the current study, we will explore whether a) supporting dietitians to implement BCC as part of standard practice influences therapeutic alliance and b) whether HNC patient outcome is mediated by therapeutic alliance. This study is embedded within an existing stepped wedge randomised controlled trial. 400 HNC patients undergoing radiotherapy will be recruited from five Australian hospital sites. Patients and dietitians will complete the five item version of the Agnew Relationship Measure during week one of radiotherapy and again four and 12 weeks post radiotherapy. Nutritional Status and Quality of Life will be assessed during the first and final week of radiotherapy and again four and 12 weeks post radiotherapy using the PG-SGA and EORTC QLQ-C30. Recruitment is due to begin November 2012. Improved understanding of the impact of relational factors on treatment outcome in HNC patients represents an important step in improving the quality of care available to this challenging patient group.