Living Reference Work Entry

Encyclopedia of Behavioral Medicine

pp 1-4

Date: Latest Version


  • Amy WachholtzAffiliated withDepartment of Psychology, University of Colorado-DenverDepartment of Psychiatry, University of Massachusetts Medical School Email author 
  • , Elizabeth GleyzerAffiliated withDepartment of Psychology, William James College


Dual diagnosis; Morbidity burden; Multifactorial disease; Multimorbidity; Patient complexity; Polymorbidity


Comorbidity is the presence of more than one distinct condition in an individual (Valderas et al. 2009).


Often, the term comorbidity refers to the presence of an index condition and other unrelated conditions (Starfield 2006). An index condition or disease describes the main condition under study (Ording and Sørensen 2013). Related terms, such as dual diagnosis and multimorbidity, are used in various clinical and research settings. Dual diagnosis is usually defined specifically as coexisting mental illness and substance or alcohol use disorders. Multimorbidity refers to the co-occurrence of multiple chronic or acute conditions in one person without identifying an index condition (Valderas et al. 2009). Depending on the setting and application of the concept, such as in clinical care, epidemiology, or health services planning and finances, clinicians may ...

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