Pneumonia is one of the leading causes of death among children younger than 5 years. The Pneumonia Etiology Research for Child Health (PERCH) study reports the results of a case–control study to characterize the causes of childhood pneumonia. The researchers enrolled children aged 1–59 months without HIV infection who were admitted to hospital with severe pneumonia. The study included sites in seven countries in Africa and Asia in low-income and lower-middle-income settings. The results of the study revealed that ten pathogens were responsible for 79–90% of cases, viruses accounted for ~61% of pneumonia and bacteria accounted for ~27%. In particular, respiratory syncytial virus (RSV) was the most common cause of pneumonia at all sites, accounting for ~31%. The findings have implications for the prevention and treatment of pneumonia in those areas and underscore the importance of the development of an RSV vaccine.