Family interventions in anorexia nervosa (AN) have been developed to ameliorate maladaptive patterns of patient-carer interaction that can play a role in illness maintenance. The primary aim of this study is to examine the inter-relationship between baseline and post-treatment distress in dyads of carers and patients with AN to examine the interdependence between carers and patients. The secondary aim is to examine whether a carer skills intervention [Experienced Carer Helping Others (ECHO)] impacts on this inter-relationship. Dyads consisting of treatment-seeking adolescents with AN and their primary carer (n = 149; mostly mothers) were randomised to receive a carer skills intervention (ECHO) in addition to treatment as usual (TAU), or TAU alone, as part of a larger clinical trial. Carers and patients completed a standardised measure of psychological distress (The Depression, Anxiety, and Stress Scale) at baseline and 12 months post-treatment. The Actor Partner Interdependence Model was used to examine longitudinal changes in interdependence by treatment group. As expected, post-treatment levels of distress were related to baseline levels in both groups (actor effects). Moreover, carer distress at 12 months was related to patient distress at baseline for the TAU (partner effects), but not for the ECHO group. Finally, carers' distress change was not a significant predictor of patients' body mass index (BMI) change in the two treatment conditions. These findings are limited to predominantly mother-offspring dyads and may not generalise to other relationships. The ECHO intervention which is designed to teach carers skills in illness management and emotion regulation may be an effective addition to TAU for ameliorating interdependence of distress in patients and their primary carers over time.