Pain is not a subjective experience, it is, particularly in children, an emotional issue. The formation of the International Association for the Study of Pain (IASP) in 1973 injected some standards and objectivity into the subject which allowed investigators around the world to probe both the underlying scientific basis of pain and nociception (nociception being the noxious sensation per se with no regard to the emotional experience). At the same time therapeutic strategies for different clinical problems have been evaluated, putting pain management on a scientifically secure and more individually effective basis. Self report has been the 'gold standard' of pain measurement but even in co-operative adults this has inherent weaknesses/biases related to the person and their situation (both the feelings and the reporting of pain are context sensitive). In some clinical areas, subject report is clearly impossible e.g. the psychogeriatric population, the mentally retarded and in preverbal children. However, even in these groups, there are usually behavioural responses to acute pain that are reasonably interpretable by their caregivers.