BACKGROUND Purulent pleurisy has become rare. It is often masked by previous antibiotic treatment so that functional prognosis may be poor. PATIENTS AND METHODS Twenty children with purulent pleurisy of the large cavity admitted from 1987 to 1993 were included in the study: there were nine infants (age 5 to 18 months) with pleuro-pulmonary staphylococcal infection (group I) and 11 children (4-13 years) (group II). Clinical, biological, bacteriological and radiologic findings were analysed retrospectively as was the outcome. RESULTS Patients of group I were admitted in poor general condition. X-ray showed moderate effusion and characteristic signs of staphylococcal infection. The bacteria identified in seven patients (77%) was S aureus. Recovery was rapid with antibiotics and simple local treatment. X-rays were normal two months after hospital discharge in seven patients (77%). One infant presented cicatricial bullous emphysema which required segmental resection. Patients of group II were admitted for moderate respiratory signs after a relatively long delay (14 days) since the onset of symptoms. X-rays showed considerable effusion in all and mediastinal shift in five patients (45%). Streptococcus pneumoniae was identified in one patient only. Local treatment of empyema was difficult; the effusion, already fibrinous, required repeated use of chest tubes in eight cases and surgical decortication in three. X-rays, performed 2 months after hospital discharge, were normal in only three patients. Long-term course was nevertheless favorable since chest X-rays at 5 months were normal in all children of both groups. CONCLUSIONS Early recognition of purulent pleurisy is important in children aged over 3 years to ensure effective drainage before the effusion becomes fibrinous. All patients in whom the first tube was inserted after more than 10 days had a difficult follow-up requiring repeated chest drainages or surgery. Ultrasonography was a useful aid for diagnosis and local treatment. Computed tomography was useful for adapting treatment after several days of course.