The main features are multiple, recurrent and frequently changing physical symptoms of at least two years duration. Most patients have a long and complicated history of contact with both primary and specialist medical care services, during which many negative investigations or fruitless exploratory operations may have been carried out. Symptoms may be referred to any part or system of the body. The course of the disorder is chronic and fluctuating, and is often associated with disruption of social, interpersonal, and family behaviour. Short-lived (less than two years) and less striking symptom patterns should be classified under undifferentiated somatoform disorder.