A judgement may be defined as an assertion made with evidence or good reason in a context of uncertainty. In psychiatry the uncertainty is inherent in the professional context and the evidence derives from academic literature and scientific studies as they are applied to a specific patient. The nature of the uncertainty and the factors that should inform professional judgement are explored in this article. Professional judgement currently faces two serious challenges: an obsession with numbers, which comes from within medicine, and the ‘patient choice’ agenda, which is politically inspired and comes from outside medicine. In this article we strive to defend professional judgement in the clinic against both challenges.