Hospital records of 116 children under 5 years of age discharged from 11 hospitals in three regions in England with a diagnosis of lobar (pneumococcal) pneumonia were reviewed to estimate the proportion likely to be attributable to infection with Streptococcus pneumoniae. Of these, 100 (86%) had lobar/focal changes on chest X-ray consistent with pneumococcal infection, although only one (1%) had pneumococcus isolated from blood. However, a further 89 (89%) with a lobar/focal picture were considered to be likely or possibly due to pneumococcal infection on the basis of the white cell count, level of C-reactive protein, isolation of the S. pneumoniae from either sputum or nasopharingeal aspirate and failure to identify another responsible pathogen. Of 135 cases with a discharge diagnosis of bronchopneumonia or pneumonia (organism unspecified), two (1%) had S. pneumoniae isolated from blood and a further 95 (70%) had clinical or laboratory features consistent with pneumococcal infection or S. pneumoniae isolated from either sputum or nasopharyngeal aspirate. With the imminent availability of conjugate pneumococcal vaccines, there is a need for improved diagnostic methods for identifying the pathogens responsible for community-acquired pneumonia in young children.