OBJECTIVE: In 2012, the Centers for Medicare and Medicaid Services implemented a policy that penalizes hospitals for "excessive" all-cause hospital readmissions within 30 days after discharge from an index hospitalization for heart failure (HF), acute myocardial infarction (AMI), and pneumonia. The aim of this study was to investigate the influence of psychiatric comorbidities on 30-day all-cause readmissions following hospitalizations for HF, AMI, and pneumonia. METHODS: Data from 2009-2011 were derived from the HMO Research Network Virtual Data Warehouse of 11 health systems affiliated with the Mental Health Research Network. All index inpatient hospitalizations for HF, AMI, and pneumonia were captured (N=160,169). Psychiatric diagnoses for the year prior to admission were measured. All-cause readmissions within 30 days of discharge were the outcome variable. RESULTS: Approximately 18% of all individuals with index inpatient hospitalizations for HF, AMI, and pneumonia were readmitted within 30 days. The rate of readmission was 5% greater for individuals with a psychiatric comorbidity compared with those without a psychiatric comorbidity (21.7% and 16.5%, respectively, p<.001). Depression, anxiety, and dementia were associated with more readmissions of persons with index hospitalizations for each general medical condition and for all the conditions combined (p<.05). Substance use and bipolar disorders were linked with higher readmissions for those with initial hospitalizations for HF and pneumonia (p<.05). Readmission rates declined overall from 2009 to 2011. CONCLUSIONS: Individuals with HF, AMI, and pneumonia experience high rates of readmission, but psychiatric comorbidities appear to increase that risk. Future interventions to reduce readmission should consider adding mental health components.