Pain is a complex neuro-physiological phenomenon affecting mind and behaviour, and is in turn also affected by psyche and behaviour. Differences among individuals in modulation, interpretation and expression complicate the comparison of pain between patients. Pain is a subjective experience and can be expressed by the patient in many different ways. In addition, influential factors from a bio-psycho-social perspective have to be taken into consideration: the interaction among somatic, psychological and social factors determines the ultimate pain experience and pain behaviour. Measuring pain therefor requires a multi-dimensional approach in which the pain, observed from various levels, and the associated problems can be determined.