Community-acquired pneumonia is one of the most common serious infections in children, with an annual incidence of 34 to 40 cases per 1,000 children in Europe and North America. When diagnosing community-acquired pneumonia, physicians should rely mainly on the patient's history and physical examination, supplemented by judicious use of chest radiographs and laboratory tests as needed. The child's age is important in making the diagnosis. Pneumonia in neonates younger than three weeks of age most often is caused by an infection obtained from the mother at birth. Streptococcus pneumoniae and viruses are the most common causes in infants three weeks to three months of age. Viruses are the most frequent cause of pneumonia in preschool-aged children; Streptococcus pneumoniae is the most common bacterial pathogen. Mycoplasma pneumoniae and Chlamydia pneumoniae often are the etiologic agents in children older than five years and in adolescents. In very young children who appear toxic, hospitalization and intravenous antibiotics are needed. The symptoms in outpatients who present with community-acquired pneumonia can help determine the treatment. Knowing the age-specific causes of bacterial pneumonia will help guide antibiotic therapy. Childhood immunization has helped decrease the incidence of invasive Haemophilus influenzae type B infection, and the newly introduced heptavalent pneumococcal vaccine may do the same for Streptococcus pneumoniae infections.