We present a 3-year-old boy with an elastin gene mutation and multiple peripheral pulmonary stenoses, who developed aneurysms of the pulmonary arteries spontaneously. We performed transcatheter occlusion of the aneurysms with detachable coils. While pulmonary arterial aneurysms may develop following pulmonary balloon angioplasty, spontaneous development is exceedingly rare. To the best of our knowledge, this is the first report describing spontaneous development of pulmonary artery aneurysms in a patient with peripheral pulmonary artery stenoses due to mutation of the elastin gene or Williams-Beuren syndrome.