Functional disorders (FDs) are physical symptoms that trigger the sufferer to seek healthcare but remain unexplained after appropriate medical assessment. They are common and cause significant distress and disability. What doctors say and do, and the design of the healthcare system, play key roles in aetiology. When patients present with physical symptoms, it is important to rule out serious physical pathology. However, early ‘positive’ diagnosis of FDs can lead to better outcomes than diagnosis by exclusion.