In children, pneumonia must be differentiated from bronchiolitis and asthma. Pneumonia is the only one of these three conditions for which antibiotics are indicated. Clinical signs are more useful than radiological or laboratory investigations for differentiating pneumonia from bronchiolitis and asthma. A child has pneumonia if s/he has tachypnoea or indrawing and is not wheezing. The child's age and the severity of the illness episode predict the aetiology of the pneumonia. The majority of children with community-acquired pneumonia can be managed in primary care. The antibiotic of choice for children < or = 5 years of age is oral amoxycillin and for older children and adolescents is oral erythromycin. Antibiotics will not prevent pneumonia in a child with an upper respiratory tract infection. Up to 80% of adults with pneumonia can be managed as outpatients. Indicators of morbidity and mortality from pneumonia are well described. Clinical features and radiology do not reliably predict the causative agent in adults with pneumonia, thus initial treatment is empirical. Streptococcus pneumoniae is the most common cause of pneumonia in all studies. The initial antibiotic treatment should be active against this organism. Penicillin oramoxycillin or erythromycin are all suitable. Erythromycin has the advantage of being active against Mycoplasma pneumoniae and Legionella species. Follow-up of patients is important to decide whether they are responding to the empirical treatment.