This best practice guidance, based on existing strategies, is for primary care trust and prison partnership boards to consider when devising, implementing and monitoring constant observation practice in establishments. The guidance is drawn from evidence based best practice guidelines and existing strategies across both the prison and mental health services, and whilst some of these guidelines were drawn up for acute mental health settings, they would equally apply across custodial services, where there is a duty of care placed on the service. (DH - letters)