To examine the odds associated with having medical comorbidities among patients with serious mental illness (SMI) in a large integrated health system. In a secondary analysis of electronic health record data, this study identified 25,090 patients with an ICD-9 SMI diagnosis of bipolar disorder (n=20,308) or schizophrenia (n=4782) and 25,090 controls who did not have a SMI, matched on age, gender, and medical home facility. Conditional logistic regressions compared the odds associated with having nine medical comorbidity categories and fifteen chronic or serious conditions among patients with SMI versus controls. Results showed having a SMI was associated with significantly higher odds of each medical comorbidity examined (p’s<0.001), except no evidence of a significant association was found between having schizophrenia and musculoskeletal diseases. A similar pattern was found regarding the chronic or severe conditions, where having schizophrenia or bipolar was associated with >1.5 times the odds of each condition (p’s<0.001). In an integrated health system where patients may have fewer barriers to care, SMI patients are likely to present for treatment with a range of medical comorbidities, including chronic and severe conditions. SMI patients may need outreach strategies focused on disease prevention, screening and early diagnosis, and treatment to address medical comorbidities and associated poor health outcomes.