To evaluate group supervision implementation fidelity in the Strengths Model of case management within one adult mental health service. A fidelity audit was undertaken to analyse data across three service settings-residential and community-during the initial three months, utilising instruments developed by Rapp and Goscha (The Strengths Model: Case management with people with psychiatric disabilities, vol 2. Oxford University Press, New York, 2006). Very high fidelity for group supervision was achieved for group interaction (74.8%), client work (77%) and by case managers (90%). A standardised approach to group supervision process and documentation greatly supported fidelity in implementation. The Rapp and Goscha tools had utility as both learning aids and audit instruments.