Hypnosis is a technique whereby an individual can reach a particular state, quite unrelated to sleep, characterized by aroused, attentive and focused concentration. Although there are numerous clinical applications of hypnosis, there are virtually no controlled clinical trials to support its effectiveness. We propose a controlled randomized clinical trial comparing a "control" group of chronic pain patients treated by a programme including conventional oral medication combined with various nerve blocks and/or spinal administration of drugs, with a "treatment" group having a similar treatment programme plus hypnosis carried out by nurses. Outcome measurements include mainly the variation of pain intensity, the amount of analgesic drug consumption, spontaneous physical activity, and the change in health-related quality of life. The assessment of the outcome variable is done at the initial workup, weekly for the first 3 weeks, and at 6 and 12 weeks. A follow-up survey is conducted at 6 months.