A case of acquired pulmonic stenosis is described. The only symptoms reported by the patient, a seemingly healthy woman, were minor chest discomfort and mild dyspnea upon exertion for the last six month. Cardiac catheterization revealed stenoses of both the right and left pulmonary arteries. Magnetic resonance imaging revealed a mediastinal tumor mass that almost totally compressed the right main pulmonary artery and also encroached upon the left pulmonary artery. Histologically the tumor was a malignant teratoma. The subsequent course of treatment was complicated by cardiac tamponade. With regression of the tumor during therapy the signs of pulmonic stenosis disappeared. In cases with acquired pulmonic stenosis an underlying mediastinal tumor has to be considered.