Introduction: Research has shown that electronic platforms can assist data capture of patient-reported outcome measures (PROMs) to guide clinical care. In comparison, routine collection of carer-reported outcome measures (CROMs) to support the patient-carer dyad during cancer treatment has had limited attention. The current study utilised a novel electronic CROM (eCROM) system, ScreenIT Carer, to monitor the prevalence and nature of distress in carers of patients undergoing (chemo)radiotherapy ((C)RT) for head/neck cancer (HNC), and explore factors associated with carer distress. Methods: Carers completed ScreenIT Carer weekly when attending patients' (C) RT treatment sessions from planning to 2 weeks post-treatment. ScreenIT Carer included the Distress Thermometer (DT) and Problem List, and a purposebuilt Mealtime-Specific DT and Problem list. Data were first examined descriptively, then associations between demographic/treatment-related factors and distress severity were analysed using mixed-effects general linear modelling. Results: 135 carers provided 434 ScreenIT Carer entries during the study period (mean entries = three/carer; yielding average adherence rate of 41% (range 11-100%)). A high prevalence of general (59%) and mealtime-specific distress (46%) was reported by carers. Nature of distress was multifactorial, with emotional problems and the patients' physical condition/symptoms common contributing factors. Based on multivariate analysis, tumour site, geographical location of residence and time during (C)RT when ScreenIT Carer was completed were significant predictors of carer distress severity. Conclusions: Carer distress is prevalent and multifactorial during (C)RT. This study highlights the feasibility of utilising eCROM platforms such as ScreenIT Carer, to monitor carer wellbeing and guide supportive care services as part of a holistic care pathway.