A prospective study of community-acquired pneumonia in Hong Kong was carried out between January and December, 1988. Ninety adults (57 male) with a mean age of 57.3 years were admitted to the Prince of Wales Hospital with community-acquired pneumonia. The etiologic diagnosis of pneumonia was made in 37 cases (41 percent). Pneumococcal infection was diagnosed in 11 patients (12 percent). The same number of patients had pulmonary tuberculosis presenting as acute pneumonia. It could not be differentiated from other causes of pneumonia on clinical and radiologic grounds, although pleural effusion and upper lobe involvement were more common in patients with tuberculosis. Chlamydia species were identified in five patients (6 percent) and Mycoplasma pneumoniae was identified in three patients (3 percent). There was no case of Legionnaires' disease. The etiologic agent could not be identified in 59 percent of cases. The low incidence of etiologic diagnosis of community-acquired pneumonia was probably related to the widespread use of antibiotics in private practice. Tuberculosis is an important cause of community-acquired pneumonia in Hong Kong and this diagnosis should be considered in patients who fail to respond to first-line antibiotics.