Brain natriuretic peptide (BNP) is a strong prognostic predictor in congestive heart failure patients. Community-acquired pneumonia (CAP) is frequently associated with systemic inflammatory response syndrome (SIRS), evolving into septic shock, with high mortality. The aim of this study was to compare BNP mean values in CAP, chronic obstructive pulmonary disease (COPD) exacerbation, and acute bronchitis patients, and to evaluate the correlation of BNP values with length of hospital stay. In all, we analysed 56 patients (28 males and 28 females) admitted to our Emergency Department from May 2010 to April 2011 because of dyspnea. The CAP patients had significantly higher mean BNP values in comparison to acute bronchitis patients (127.2 Vs 45.9 pg/mL; p=0.003), and a significantly positive correlation was found between their BNP values and length of hospital stay (r=0.404; p=0.05). A stepwise multivariate linear regression analysis model showed white blood cell count as the only independent predictor of length of hospital stay (p=0.05). The results suggest that CAP patients with SIRS have increased mean BNP levels compared to acute bronchitis patients, but this parameter failed to predict the length of hospital stay.