Diagnoses play vital roles in child and adolescent mental health services and research. They facilitate accurate communication, selection of appropriate interventions and estimation of prognosis. Receipt of a diagnosis can generate relief and improved understanding for many families. However, a diagnosis can also lead to feelings of loss or serve as a focus for stigma. Difficulties are magnified when public discourse generates and propagates misunderstandings. These include a failure to appreciate that current diagnostic categories are syndromes (clusters of symptoms and signs) that lack distinct biological signatures or clear demarcation from healthy variation. Even within a single diagnosis, heterogeneity and developmental change are typical. Whilst diagnoses are important, scientists and practitioners need to be able to describe to the public that mental ill health does not consist of a set of distinct diagnostic categories and that many diagnoses lie on a spectrum of severity including less severe psychopathology that cannot be equated with a clinical diagnosis. This perspective emphasises the appropriateness of stepped care, where intensity of treatment, provision of diagnosis and specialist involvement vary across the spectrum.