Streptococcus pneumoniae is the most frequent pathogen of severe community-acquired pneumonia (CAP) necessitating hospitalization. The main objective of this multicentre prospective study was to determine the value of clinical, biological, and radiological features for predicting pneumococcal etiology and to define prognostic factors. Streptococcus pneumoniae was isolated in 43/132 patients (33%) with CAP requiring ICU treatment. The mean age of the patients with pneumococcal pneumonia was 55 +/- 17 (SD) yrs and 34 were male. On admission, 14 patients with pneumococcal pneumonia were in shock, 24 were mentally confused, and 27 required mechanical ventilation during their hospitalization. Among the clinical, biological, and radiological features, fever > 39 degrees C, pleuritic chest pain, lobar distribution or alveolar consolidation, and an increase in immature granulocytes > or = 5% of WBC were more frequent in pneumococcal pneumonia than in other etiologies. Mortality was 35%. Fatal outcome was significantly related to the presence of impaired alertness, septic shock, mechanical ventilation, acute renal failure, and bacteremic pneumonia.