Pain is a complex, multidimensional experience that has at least two major components. The first, nociception, is a sensory component directly related to activity in neural pathways responsive to tissue damage. The second is the complex psychologic, physiologic, emotional, and behavioral response to the nociception. This response is determined by many intrinsic and extrinsic factors. In general, children will have less pain when the exacerbating factors, which are outlined in Table 1, are minimized. Because pain is experienced individually and subjectively, assessment of pain in each individual is essential. Assumptions regarding an individual's pain should not and cannot be inferred from the amount of tissue damage he or she has experienced. Therefore, regarding assessment of pain in children with cancer, the following principles were agreed upon. 1. Systematic assessment of pain should be considered idered a necessary part of the management of cancer. Most children with cancer will be at risk for significant pain at some time during the course of their illness. Such pain can be caused by the disease itself, by invasive diagnostic and monitoring procedures, and by treatment. Therefore, adequate care must include a plan for comprehensive assessment ent and management of all forms of pain in addition to the disease-management protocol. 2. Assessment of pain must be ongoing throughout the course of the illness. Sources of nociception and modifying factors will change through time and must be evaluated continuously. MEASUREMENT OF PAIN Although comprehensive assessment of pain must include more than measurement of intensity or severity, this aspect of pain is important and has been studied the most widely.