Physical-mental comorbidity is often associated with worse clinical and psychosocial outcomes, reduced health-related quality of life, and increased healthcare utilization. The following article is dedicated to the health economic aspects of physical-mental comorbidity. It presents basic theoretical and methodological aspects of cost-of-illness studies and economic evaluations related to physical-mental comorbidity, which are explained and discussed for the practical example of comorbid depression in diabetes mellitus. The results show that mental comorbidity in diabetes is associated with increased healthcare costs, which can in part be attributed to an increased somatic health service use. Appropriate interventions can lower these excess costs. Economic evaluations assessing the effectiveness of interventions for depressive diabetics have shown that overall health can be improved and costs saved. However, especially in health economics, mental comorbidity in somatic diseases has not been comprehensively investigated and further research is warranted.
