OBJECTIVES:  To explore and quantify the association between MRSA/MSSA infection and readmission risk among patients with pneumonia. METHODS: Healthcare Cost and Utilization Project-State Inpatient Databases were used to identify all inpatient admissions with a primary diagnosis of pneumonia in Florida (2009-2013), Massachusetts (2010-2012) and California (2009-2011). Readmissions were measured by the CMS validated algorithm. MRSA and MSSA infections as secondary diagnoses were identified with ICD-9-CM codes. All pneumonia patients were categorized into three subgroups: MRSA-infected, MSSA-infected and non-MRSA/MSSA. Descriptive analysis was performed to compare demographic differences across three groups, and multivariate logistic regression was applied to evaluate the association between MRSA/MSSA infection and probability of readmission. RESULTS: Among 450,793 inpatient admissions with pneumonia, 2,285 (0.51%) had MRSA and 996 (0.22%) had MSSA. Compared to patients in the non-MRSA/MSSA group, patients in the MRSA group had higher Medicare coverage (72.56% vs 66.47%) and longer length of stay (LOS) (7.17 vs 5.36 days), while patients in the MSSA group were younger (65.51 vs 68.43 years old), predominantly male (56.48% vs 47.56%), had higher Medicaid coverage (12.25% vs 9.90%) and longer LOS (8.84 vs 5.36 days) (all p <0.05). Compared with non-MRSA/MSSA group (18.09%), the readmission rates wee higher in the MRSA (28.45%) and MSSA groups (23.80%) (all p<0.001). Controlling for demographic and illness factors, MRSA infection was associated with a higher risk of readmission (OR=1.497, p<0.001), while MSSA infection was also a risk factor for readmission (OR=1.201, p<0.018). Older age (OR=1.006, p<0.001), African American (OR=1.202, p<0.001, ref=whites), homeless status (OR=1.935, p<0.001) and longer LOS (OR=1.058, p<0.001) were associated with greater readmission risk, while female (OR=0.883, p<0.001) and private insurance (OR=0.668, p<0.001, ref=Medicare) were associated with lower readmission risk. CONCLUSIONS: MRSA/MSSA infection among pneumonia patients was associated with a higher risk of readmission. Programs to reduce the risk for MRSA/MSSA infection at discharge would likely reduce readmissions.