Purpose: The caregiver roles and responsibilities scale (CRRS) was developed to facilitate formal assessment of broad life impacts for informal (i.e. unpaid) caregivers to people with cancer. Here we report the development and initial validation.; Methods: The CRRS was developed from the thematic analysis of two interview studies with cancer patients (stage III-IV breast, gynaecological, lung or melanoma) and caregivers. In the evaluation studies, participants completed the CRRS alongside the Caregiver Quality of Life-Cancer, the main criterion measure for concurrent validity, and the WHOQOL-BREF for additional convergent validity data. Questionnaires were completed at baseline, 7-days and 2-months. Demographic data and patient characteristics were collected at baseline.; Results: Two-hundred and forty-five caregivers to people with stage I-IV breast, colorectal, gynaecological, head and neck, lung or renal cancer or melanoma completed the CRRS at least once. The final 41 core items selected comprised five subscales: Support and Impact, Lifestyle, Emotional Health and Wellbeing, Self-care and Financial Wellbeing as well as three standalone items. Missing data rate was low (0.6%); there were no ceiling or floor effects for total scores. Cronbach's alpha was 0.92 for the CRRS-41; 0.75-0.87 for the subscales. CRRS showed good test-retest reliability (ICC = 0.91), sensitivity to change and the predicted pattern of correlation with validation measures r = 0.75-0.89. The standalone 7-item jobs and careers subscale requires further validation.; Conclusions: Initial evaluation shows the CRRS has good validity and reliability and is a promising tool for the assessment of the effects of cancer and cancer treatment on the lives and wellbeing of informal caregivers.