Experienced Carers Helping Others (ECHO) is an intervention for carers of people with eating disorders. This paper describes the theoretical background and protocol of a pilot multicentre randomised controlled trial that will explore the use of two variants of ECHO for improving outcomes for adolescents with anorexia nervosa (AN) referred for outpatient care. Adolescent patients and their carers (typically parents and close others in a supportive role) will be recruited from 38 eating disorder outpatient services across the UK. Carers will be randomly allocated to receive 'ECHOc' guided self-help (in addition to treatment as usual), 'ECHO' self-help only (in addition to treatment as usual) or treatment as usual only. Primary outcomes are a summary measure of the Short Evaluation of Eating Disorders at 6- and 12-month follow-ups. Secondary outcomes are general psychiatric morbidity of AN patients and carer, carers' coping and behaviour, and change in healthcare use and costs at 6- and 12-month follow-ups. Therapist effects will be examined, and process evaluation of ECHOc will be completed. The findings from this pilot trial will be used in preparation for executing a definitive trial to determine the impact of the preferred variant of ECHO to improve treatment outcomes for AN.