In spite of a considerable progress in comorbidity research and huge literature on it, this phenomenon is one of the greatest epistemological, research and clinical challenges to contemporary psychiatry and medicine. Mental disorders are very often comorbidly expressed, both among themselves and with various sorts of somatic diseases and illnesses. Therefore, comorbidity studies have been expected to be an impetus to research on the validity of current diagnostic systems as well as on establishing more effective and effi cient treatment within (...) the frame of person centered transdisciplinary psychiatry and integrative medicine. This review focuses fi rst on conceptual chaos and different connotations, then on transdisciplinary perspectives of comorbidity and multimorbidity. The authors compiled an extensive set of various views and perspectives, dilemmas and controversies, in order to evaluate what we know and what we don’t about comorbidity, what comorbidity is and what comorbidity is not, what are facts and what are non-facts on comorbidity and multimorbidity. (shrink)