Purpose: Head and neck cancer (HNC) patients suffer from significant morbidity, which may introduce challenging care demands and subsequent stress-induced mind-body interactions for informal caregivers. This prospective study evaluated patient and caregiver predictors of diurnal cortisol rhythm among HNC caregivers during radiation treatment. Method: Patient-caregiver dyads completed measures at radiation treatment start (T1; n = 32) and 5 weeks into treatment (T2; n = 29). Measures included the Functional Assessment of Cancer Therapy-Head and Neck, the Caregiver Quality of Life (QOL) Index-Cancer, the Caregiver Reaction Assessment, the Medical Outcomes Social Support Survey, and the Eating Assessment tool. Patients also received a clinical swallowing evaluation using the Functional Assessment of Oral Intake Scale. Caregiver cortisol concentrations were assessed from salivary samples at T1 and T2. Results: Caregiver cortisol slope became significantly flatter during radiation treatment. Greater caregiver schedule burden was associated with a flatter cortisol slope (b = .35, p = .05) in caregivers at T1. Lower patient functional QOL (b = .41, p = .05) and lower overall caregiver QOL at T1 (b = .39, p = .04) were each separately associated with a flatter cortisol slope in caregivers over treatment. Conclusions: Results suggest the presence of a mind-body interaction in HNC caregivers. Dysregulation in diurnal cortisol rhythm in caregivers was significantly associated with increased caregiver schedule burden and lower patient and caregiver QOL. Targeted interventions developed for HNC caregivers may help to prevent negative health outcomes associated with dysregulated cortisol.