Abstract Mowat–Wilson syndrome is a genetic condition due to a mutation in the ZEB2 gene; it affects many systems including the cardiovascular system. The pulmonary arterial sling originates from a failure of development of the proximal portion of the left sixth aortic arch, resulting in an anomalous left pulmonary artery origin from the posterior wall of the right pulmonary artery and the left pulmonary artery crossing to the left lung between the trachea and the oesophagus. We present a 4-month-old infant with Mowat–Wilson syndrome and left pulmonary arterial sling, and discuss the association of these two rare conditions. Pulmonary arterial sling is significantly more frequent in patients with Mowat–Wilson syndrome than in the general population.