Twenty-five patients, aged 5 months to 14 years, with acute bacterial pericarditis are reported. Thirteen (52 per cent) of the patients died. The presenting symptoms, associated illness and physical findings, bacteriology, and response to therapy are reviewed. Optimum therapy consists of intravenous administration of specific antibiotics combined with surgical drainage; 90 per cent of our patients treated in this fashion survived. Antibiotic therapy alone is usually inadequate, especially in the presence of significant effusion, and among our patients only three of 10 patients so treated survived. One patient developed constrictive pericarditis 1 month after the initial attack with meningococcal pericarditis and required pericardectomy.