BACKGROUND: Community-acquired pneumonia (CAP) is a relevant worldwide cause of morbidity and mortality in adult population, however its etiology is often not identified and therapy is empirical. AIM: To assess the etiology of CAP in immunocompetent adult hospitalized patients using conventional and molecular diagnostic methods. MATERIAL AND METHODS: We prospectively studied 240 adult patients who were hospitalized for CAP to identify the microbial etiology. Sputum and blood cultures were obtained as well as serology testing for Mycoplasma pneumoniae and Chlamydophila pneumoniae, urinary antigen testing for Legionella pneumophila and Streptococcus pneumoniae, and a nasopharyngeal swab for the detection of sixteen respiratory viruses by reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: In 100 patients (41.7%) a single respiratory pathogen was identified. In 17 (7.1%) cases, a mixed bacterial and viral infection was detected and no pathogen was identified in 123 cases (51%). The most commonly identified pathogens identified were: influenza virus (15.4%), parainfluenza virus (10.8%), rhinovirus (5%), Streptococcus pneumoniae (5%), respiratory syncytial virus (2.9%) and Mycoplasma pneumoniae (2.5%). Infectious agent detection by RT-PCR provided greater sensitivity than conventional techniques. Viral respiratory infections were more prevalent in older patients with comorbidities and high risk patients, according to the Fine index at hospital admission. The clinical severity and outcome were independent of the etiological agents detected. CONCLUSIONS: The use of molecular diagnostic techniques expanded the detection of respiratory viruses in immunocompetent adults hospitalized with CAP.