Over a three-year period, 54 episodes of pneumonia were diagnosed in 45 adults infected with the human immunodeficiency virus (HIV). These episodes were reviewed in order to assess the distribution of pathogens and their clinical presentation. Thirty-six episodes were due to an opportunistic pathogen (Pneumocystis carinii in 31, Mycobacterium avium complex in 3, Mycobacterium tuberculosis in 2), and 18 were caused by non-opportunistic pathogens (11 Streptococcus pneumoniae, 2 Haemophilus influenzae, 5 unknown pathogens that responded to broad-spectrum antibiotics). Non-opportunistic pneumonias were characterized by an abrupt onset (18/18 had pulmonary symptoms of less than 7 days duration), high fever (13/18), and focal lung infiltrates (17/18). In contrast, opportunistic infections infrequently presented with pulmonary symptoms of less than 7 days duration (3/36) or high fever (7/36), and most of the chest radiograms (34/36) disclosed a diffuse lung infiltrate. In HIV-infected patients presenting with pneumonia, simple clinical and radiological data may point to bacterial pathogens. Such data could be used in selected cases to spare invasive procedures and to start empirical antibiotic therapy.