Open Dialogue is a need‐adapted approach to mental health care that was originally developed in Finland. Like other need‐adapted approaches, Open Dialogue aims to meet consumer’s needs and promote collaborative person‐centred dialogue to support recovery. Need‐adapted mental health care is distinguished by flexibility and responsiveness. Fidelity, defined from an implementation science perspective as the delivery of distinctive interventions in a high quality and effective fashion is a key consideration in health care. However, flexibility presents challenges for evaluating fidelity, which is much easier to evaluate when manualization and reproducible processes are possible. Hence, it remains unclear whether Open Dialogue and other need‐adapted mental health interventions can be meaningfully evaluated for fidelity. The aim of this paper was to critically appraise and advance the evaluation of fidelity in need‐adapted mental health care, using Open Dialogue as a case study. The paper opens a discussion about how fidelity should be evaluated in flexible, complex interventions, and identifies key questions that need to be asked by practitioners working in need‐adapted mental health care to ensure they deliver these interventions as intended and in an evidence‐based fashion.