The concept of ‘looping effects’ helps to clarify how psychiatric conditions are moving targets. As professional understandings of mental disorders change, people shape their behaviour, experience and self-understanding in response. By this means, evolving concepts of mental disorder, carried by language, arose make up new kinds of person. The superordinate concept of ‘mental disorder’ is also a moving target. This article develops an account of the concept’s semantic alterations, proposing that it has progressively expanded horizontally to encompass qualitatively new forms of distress and disability, and also vertically to encompass quantitatively less severe phenomena. Changes in the concept of mental disorder in successive editions of the Diagnostic and Statistical Manual of Mental Disorders are examined to show that its meaning has not so much looped as spread in an ever-expanding vortex. Possible looping effects of this conceptual creep are discussed.