A 7-year-old boy presented with productive cough and mild dyspnea. He had a history of intlermittant attacksof broanchopneumonia, but otherwise he was healthy. He had a small right lung on chest roentgenogram. Thediagnosis of developmental hypoplasia of the right lung due to congenital absence of the right pulmonary arterywas made by radionuclide angiocardiography and subsequently confirmed by cardiac catheterization and angiography.