Introduction: Respiratory syncytial virus (RSV) is a major cause of pneumonia in infants worldwide. We aimed to evaluate the clinical course of community-acquired RSV pneumonia in newborns hospitalized in neonatal intensive care unit. Materials and Methods: All the newborns diagnosed as pneumonia were prospectively evaluated for RSV infection between November 2010 and April 2011. Fifty-four specimens of nasopharyngeal secretions were tested in parallel with the RAT and the multiplex real time polymerase chain reaction (RT- PCR). Downes' score was used to assess the disease severity in patients with pneumonia. Results: RAT has a sensitivity of 90% and a specificity of 78.5%, as the PCR technique target assay. Four of the patients with RSV pneumonia had secundum atrial septal defect (ASD) and all of four needed mechanical ventilation support. The first day Downes' score was positively correlated with time of intravenous fluid requirement (p= 0.001, r= 0.48), total oxygen need (p= 0.000, r= 0.63), and re-enteral feeding (p= 0.001, r= 0.46). Blood pH (p= 0.031, r= 0.46) were negatively correlated with Downes' score. The second day Downes' score was higher in patients with ASD than those of without ASD (3.8 ± 2.6 vs. 2 ± 1.1, p= 0.01). The most possible risk factor for longer hospital stay was the higher second day Downes' score (p= 0.02 OR: 1.9, CI 95% (1.1-3.2). All infants were discharged from hospital in a good health. Conclusion: RAT is sensitive and specific in detecting RSV infections in newborns. Physicians may use Downes' score for evaluation of disease severity in infants with RSV pneumonia. In these patients, ASD has increased the disease severity.