Human immunodeficiency virus (HIV) infection is associated with abnormalities of humoral immunity that result in an increased incidence of bacterial pneumonia. From 2% to 10% of acquired immunodeficiency syndrome (AIDS)-associated pneumonia is caused by encapsulated bacteria. Clinical features are usually typical of community-acquired pneumonia and include fever, productive cough, and chest pain. Focal radiographic infiltrates, an elevated WBC count, and mild hypoxemia are commonly observed. Streptococcus pneumoniae, Haemophilis influenzae, other Streptococcus species, and Branhamella catarrhalis are the predominant organisms. Bacteremia is frequent, especially with S pneumoniae infections. Despite a rapid response to antibmicrobial agents, many patients experience recurrences. Prevention of bacterial infections with prophylactic antibiotics and immunizations is recommended for selected HIV-infected patients.