Objective: The aim of this study was to develop and validate a new ques- tionnaire designed to measure caregiver skills that, in line with the interperso- nal component of the cognitive inter- personal maintenance model (Schmidt and Treasure, J Br J Clin Psychol, 45, 343–366, 2006), may be helpful in the support of people with anorexia nerv- osa (AN). A further aim is to assess whether this scale is sensitive to change following skills-based caregiver interventions.Method: The Caregiver Skills (CASK) scale was developed by a group of clinicians and caregivers. Preliminary versions of the scale devised for both caregivers and parents were given at baseline and at follow-up after two studies of caregiver interventions (a clinical trial of the effec- tiveness of guided self-help and training workshops). Exploratory and confirmatory factor analyses (CFA) were used to test the factorial structure of the CASK scale. Cron- bach’s alpha was used to measure inter- nal consistency of the CASK scales.Results: Exploratory Factor Analysis sug- gested a six component solution (Bigger Picture, Self-Care, Biting-Your-Tongue, Insight and Acceptance, Emotional Intelli- gence and Frustration Tolerance) and this model was confirmed with CFA. Signifi- cant clinically relevant correlations were found between the CASK scales and other standardised measures of caregiv- ers’ attitudes and behaviours. Further- more, greater improvements on abilities measured by the CASK scale were found in caregivers who received skills-training than caregivers assigned to a ‘treatment as usual’ condition.Discussion: The CASK scale is a measure of the fidelity of interventions based on the cognitive interpersonal maintenance model and is sensitive to the intensity of the intervention provided.