Twenty-five patients with main and peripheral pulmonary artery stenosis were studied to determine the most frequently observed diagnostic sign of this abnormality regardless of the underlying etiologies, such as intrinsic or extrinsic narrowing of the pulmonary artery due to tumor, fibromuscular dysplasia, thromboembolism, angitis including the aortitis syndrome (Takayasu arteritis) and a variety of other disease entities. Among a variety of signs and symptoms, we emphasized the importance of cardiac auscultation and phonocardiography, which were often the initial diagnostic clues. The diagnostic features included a systolic murmur of pulmonary arterial origin and the behavior of the splitting of the second heart sound. The systolic murmur was often trans-systolic or continuous. In cases with left-sided cardiac murmurs (Takayasu arteritis, etc), the pulmonary systolic murmurs were not identified by auscultation alone and required phonocardiographic confirmation. In many cases the second heart sound was split and this was sometimes the first clue to the diagnosis. The split intervals varied, but were more marked in cases with pulmonary hypertension, and were accompanied by the accentuated pulmonic component (IIP). Phonocardiographic analysis disclosed that wide splitting was caused by the delayed appearance of IIP as well as the concomitant early appearance of the aortic component (IIA). It was concluded that, although the final etiological diagnosis is not identified, auscultation and phonocardiography provide important clues for further diagnostic and etiological studies of pulmonary artery stenosis.