Background: Cardiac Troponin iso-enzyme I (cTnI) is known as a specific biomarker of myocardial damages. CTnI rises in various systemic non-cardiac diseases and assumed as an important prognostic factor. Excluding the patients presenting with acute cardiac problems, in this study we investigated the relationship between serum cTnI elevation and the severity of disease in hospitalized patients with CAP. Methods: From March 15, 2014 to April 2015, through a prospective cohort study, hospitalized patients with CAP were included. Patient were excluded if: recent hospitalization with possibility of hospital acquired pneumonia; on admission intubation; ABG obtained after two hours of admission; ABG obtained while the patient was on supplemented oxygen. Patients, with previous or current history of congestive heart disease and those with clinical and ECG finding compatible with acute coronary syndrome, acute pericarditis or acute myocarditis and those with associated renal failure were excluded. CTnI was obtained on admission and 3rd day and CURB-65 and pneumonia severity index (PSI) were calculated for each patient. Results: Of 65 patients, 27 patients were included (M/F: 15/12, Age: 64.2 ± 14.4 yrs). Troponin was positive in 14/27. A significant correlation was found between 3rd day cTnI titer and CURB-65 (r=0.43, P=0.02) and PSI score (r=0.56, P<0.01). PSI and CURB-65 scores were significantly greater in those who the cTnI became positive at 3rd day (125.5 ± 41.7 vs. 82.2 ± 27.4; P=0.01 and 2.3 ± 1.0 vs. 1.1 ± 0.7; P=0.01 respectively). There was no significant age and gender associated cTnI importance. Conclusion: In this study significant association was found between cTnI increasing titer within first third days of hospitalization and pneumonia severity index/ CURB-65. We recommend serial monitoring of the level of this marker (at least in first 3 days) in order to predict the disease severity in hospitalized patients with CAP.