Although clinical studies and animal models seem to establish an important role for the sympathetic nervous system in many forms of neuropathic and inflammatory pain, there is an ongoing debate on the classification of pain syndromes with sympathetic components. The confusion originates from several sources: failure to acknowledge that the pathomechanism of chronic pain can change during the progress of the disease, which is now strongly underlined by experimental data from suitable animal models. Neuropathic pain is a vaguely defined collection of pain syndromes which includes painful conditions with diverse and largely unknown patho-mechanisms. Clinical diagnosis is difficult and well designed, placebo controlled sympathectomy is rarely performed. [blumberg et al.]