Abstract The experience with pericarditis at the Children's Hospital Medical Center of Boston during the past ten years is reviewed. The clinical features of the most common etiologic groups, rheumatic fever, rheumatoid arthritis, bacterial infection and the benign idiopathic group, are presented. The problem of differentiating between pericardial effusion and cardiac dilatation is considered, and the most helpful methods of diagnosis are discussed. The therapy of the more frequent etiologic forms is indicated.