Concepts of disease, illness (being ill), and criteria for issuing sickness certificate for musculoskeletal pain have been investigated by a postal survey based on case histories. Questionnaires were filled in by 898 individuals; 194 General Practitioners, 76 medical consultants working for the National Insurance Administration, 307 insurance clerks, and a representative sample (N = 321) of the general public. The concepts disease and illness are meaningful and used consistently by medical doctors for infectious disease and somatic problems. Discrepancies between the medical profession representatives and the general public were, in general, attributable to differences in information and knowledge about these somatic conditions. However, for musculoskeletal pain all groups had conceptual problems. In particular, there was a lack of consensus for issuing sickness certificates. For musculoskeletal pain conditions the doctors, as a group, seemed to score at random or 50-50 level for sickness certification. All groups, including medical doctors, were reluctant to accept depression and social problems as diseases, or to accept social problems as reasons for sickness certification. The decision criteria should be identified and systematized in order to establish whether it is possible to reach a consensus for subjective complaints.