Aberrant left pulmonary artery, or pulmonary sling, is a rare variation of the pulmonary vasculature, with only one previous report of the condition being recognized in an adult. In this report a second case recognized de novo in an adult is presented. Both of these adults were evaluated because of right paratracheal masses which required differentiation from pulmonary malignancies. The barium swallow shows a characteristic indentation of the anterior esophageal wall and the lateral tomogram demonstrates absence of the left pulmonary artery from its normal position in the left hilum. The pulmonary arteriogram is diagnostic and allows avoidance of more invasive diagnostic measures.