OBJECTIVES: To examine the association between mental illness and chronic physical conditions in older adults and investigate whether co-occurring substance use disorders (SUDs) are associated with greater risk of chronic physical conditions beyond mental illness alone.

DESIGN: A retrospective cross-sectional study.

SETTING: Medicare and Medicaid programs in Massachusetts.

PARTICIPANTS: Massachusetts Medicare and Medicaid members aged 65 and older as of January 1, 2005 (N = 679,182). MEASUREMENTS: Diagnoses recorded on Medicare and Medicaid claims were used to identify mental illness, SUDs, and 15 selected chronic physical conditions.

RESULTS: Community-dwelling older adults with mental illness or SUDs had higher adjusted risk for 14 of the 15 selected chronic physical conditions than those without these disorders; the only exception was eye diseases. Moreover, those with co-occurring SUDs and mental illness had the highest adjusted risk for 11 of these chronic conditions. For residents of long-term care facilities, mental illness and SUDs were only moderately associated with the risk of chronic physical conditions.

CONCLUSION: Community-dwelling older adults with mental illness or SUDs, particularly when they co-occurred, had substantially greater medical comorbidity than those without these disorders. For residents of long-term care facilities, the generally uniformly high medical comorbidity may have moderated this relationship, although their high prevalence of mental illness and SUDs signified greater healthcare needs. These findings strongly suggest the imminent need for integrating general medical care, mental health services, and addiction health services for older adults with mental illness or SUDs. Geriatrics Society.