Clinical, radiographic and routine laboratory features of pneumonia can offer clues to the etiologic agent of the infection, but a specific etiologic diagnosis requires the assistance of the microbiology laboratory. Diagnostic tests are controversial in the management of pneumonia. In this study, the importance of the Gram stain in microbiologic diagnosis of lower tract infections is emphasized by comparing Gram stained preparations of 2322 sputum samples with cultures and it is suggested that a reasonable approach to the diagnostic evaluation of pneumonia is attained only when interpreted according to criteria by an experienced bacteriologist.