Most adults with community-acquired pneumonia are treated as outpatients. Despite this, the majority of studies regarding community-acquired pneumonia have been in hospitalized patients only and may not be applicable to an ambulatory population. This review critically examines the literature regarding the diagnosis, cause, appropriate patient selection, and treatment of nonhospitalized adults with community-acquired pneumonia, including human immunodeficiency virus-infected individuals. English-language articles on oral antibiotic trials for community-acquired pneumonia, obtained from a MEDLINE search from 1966 to the present, are reviewed. Etiologic diagnosis is helpful in determining appropriate outpatient treatment for community-acquired pneumonia, and usually requires only sputum Gram's stain analysis. Viral, mycoplasmal, and chlamydial agents are among the most common pathogens encountered in individuals treated as outpatients, although much variability exists. Many oral antibiotic trials for community-acquired pneumonia have been published, but shortcomings in study design limit their clinical applicability. A treatment algorithm is offered, using the best available data.