Evaluation and assessment are the first steps of any strategy for the management of cancer pain, and are fundamental for any clinical research project in this field. Different clinical systems for evaluation and classification of cancer pain syndromes are available and their clinical usefulness should be tested. The measurement of pain intensity is necessary to document and assess the outcome of established and new treatments. Visual analogue scales, verbal and numerical rating scales and some multidimensional tools such as the Brief Pain Inventory and the McGill Pain Questionnaire are helpful in the assessment of cancer pain provided the limitations of their validity are considered. Specific questions arise when these tools are used in long-term repeated assessments of cancer patients. Assessment and measuring techniques deserve more investigations to optimize standard valid procedures and to enable us to exchange clinical information and produce comparable data in research.