A judgement is 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 the academic literature and scientific studies as they are applied to a specific patient. The nature of the uncertainty and the factors which should inform professional judgement are explored. Professional judgement is currently facing 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. This paper strives to defend professional judgement in the clinic against both challenges.