In this paper the chronicity of pain in non-specific pain syndromes is discussed. Experts in the study of pain with several professional backgrounds in rehabilitation are the authors of this paper. Clinical experience and literature form the basis of the paper. Non-specific low back pain and Complex Regional Pain Syndrome type I (CRPS-I) are discussed in the light of chronic pain. Many definitions of chronic pain exist. Yellow flags are important factors to identify possible chronic pain. In the acute phase of a non-specific pain complaint one should try to identify possible psychosocial inciting risk factors. Behavioural and cognitive treatment seems to be effective for chronic pain patients.