OBJECTIVES: COPD is the 4th leading cause of death among U.S. adults.  Retrospective observational studies, including outcomes research, can provide important comparative analyses to help identify optimal treatment patterns and therapies.  However, such comparisons often require multivariate analysis, propensity score matching, a comorbidity index or other methods to adjust for differences in patient characteristics. Rates reported in clinical trials often vary significantly from those observed in clinical practice. Using recent, real-world data this study was designed to identify the frequency of diagnosed comorbid conditions in the COPD population and serve as a research reference for future comparative studies. METHODS: Private practitioner medical claims (CMS1500 records) from SDI Health’s data warehouse were extracted for the period November 1, 2007 to October 21, 2008.  Patients were indexed to their first observed COPD diagnosis during the study period. Qualifying patients had 2 or more claims for COPD; a valid age and gender; and were observed in the dataset for 12 months or more from their index date. Patients could be diagnosed with COPD prior to the study period or new to the condition. Comorbid conditions of interest were defined a priori. As possible, MEDRA codes used in clinical trials were cross-walked to corresponding ICD-9 codes. All payer types were included. RESULTS: Of the 751,794 qualifying study patients, the mean age was 67.5 years (STD+/-13) and 55.4% were female. The 1 year prevalence of comorbid conditions observed was: Supraventricular Arrhythmia13.2%, Atrial Fibrillation 9.7%, Depression 9.0%, Suicide 0.1%, Insomnia 4.1%, Ischemic disease (ATPC composite) 28.8%, Metabolic Syndrome 0.4%, and Other Mental Health conditions 14.7%. CONCLUSIONS: Patients with COPD have a variety of significant comorbid conditions observed in real-world, clinical practice.  These factors can affect findings of comparative studies and are important considerations for future research.