Though stenosis of the trunk and branches of the pulmonary artery has long been reported at necropsy (Maugars, 1802; Fiirst, 1878; Schwalbe, 1909; Oppenheimer, 1938), the disorder was thought to be extremely rare. During the past decade, however, it has been recognized more often due to the introduction of cardiac catheterization and selective angiocardiography (Moller, 1953; Coles and Walker, 1956; Smith, 1958; Luan et al., 1960). In a series of 1650 cardiac catheterizations 60 examples of bilateral multiple stenosis of the pulmonary artery were reported by Agustsson et al. (1962), while in the same year Bell et al. were able to find 14 examples among 175 patients with congenital heart disease. However, angiocardiographic confirmation of the anatomy has not always been sought, and we think that the diagnosis must remain in doubt in those where the gradient as measured by catheterization has been small and not subsequently confirmed radiologically. It is our purpose to analyse the published examples, to propose a classification (Table I), to describe the clinical picture, and to present details of 9 additional patients. Of these, 6 had both cardiac catheterization and angiocardiography. Catheterization revealed the diagnosis in all, but angiocardiography demonstrated the stenosis in only 4. In 2 others angiocardiography alone was performed and the diagnosis revealed in both. In one cardiac catheterization only was carried out and a pulmonary arterial gradient was demonstrated. To date 202 patients with post-valvular stenosis of the pulmonary artery and its branches have been reported, but we have analysed only those where adequate descriptions of both the clinical features and investigations have been given. To these 108 we have added details of a further 9 patients of our own making a total of 117 (Table II).