Sixteen patients with pericarditis caused by Histoplasma capsulatum were studied. Fourteen were less than 30 years old, and no patient had an underlying illness or was receiving immunosuppressive therapy. All patients experienced a flu-like prodromal illness lasting from 2 weeks to 4 months. Pneumonitis or hilar adenopathy, or both, was found in 12; pleural effusion, uncommon in primary pulmonary histoplasmosis, was found in seven patients. Pericardial fluid, pleural fluid and bone marrow cultures yielded no growth. All patients demonstrated a fourfold or greater change in complement-fixing antibody titers. No patient had disseminated disease, and only one required treatment with ampholericin B. The illness ran a protracted course, and in six patients symptomatic pericarditis recurred. Ultimately all recovered. Ten patients were restudied 6 months to 12 years after recover. Only one patient had pericardial calcification, and none had constrictive pericarditis. This form of granulomatous pericarditis, unlike that caused by Mycobacterium tuberculosis, appears to carry a good prognosis.