OBJECTIVES: To determine the impact of comorbidity burden on real-world healthcare costs of rheumatoid arthritis (RA) patients in Turkey, using nationwide real-world data.  METHODS: Study data was obtained from MEDULA (2009-2011). Using International Classification of Disease Tenth Revision Clinical Modification (ICD-10-CM) codes, adult RA patients (ages 18-99) were identified for the identification period (June 1, 2010 - December 31, 2010). Patients were required to have two RA diagnoses at least 60 days apart, and were grouped as prevalent and incident cases. The date of the first RA claim was identified for each patient and designated as the index date. Total healthcare costs were examined over the 12-month period following the index date. To control for clinical characteristics, a comorbidity index score for each patient during the baseline period was calculated using the Elixhauser method. This index is the sum of a comprehensive set of 30 present comorbid conditions, and is widely-used in the outcomes research field to determine patient health status. Individual comorbidities, such as diabetes, respiratory diseases, allergy and cardiovascular diseases, were identified using ICD-10 codes. RESULTS: A total of 2,613 patients met all inclusion criteria (693 incident; 1,920 prevalent patients). Prevalent patients had higher comorbidity index scores relative to incident patients. Nearly 35% of incident and 40% of prevalent patients had at least one cardiovascular, diabetic, respiratory, or allergy comorbid condition prior to the diagnosis. The mean Elixhauser Comorbidity Index score was calculated as 5.31 for incident and 5.7 for prevalent patients. Prevalent patients with respiratory and cardiovascular comorbid conditions incurred additional healthcare costs of €302 and €283 respectively. For incident patients, respiratory comorbid conditions increased the healthcare costs with €916.    CONCLUSIONS: Respiratory comorbid conditions were associated with healthcare costs for both prevalent and incident RA patients in Turkey.