Case report of unilateral pulmonary artery agenesis (UPAA) which is a rare congenital anomaly based on current literature. We present the case of a 26-year old man who was admitted to our department for evaluation of an abnormal chest x-Ray (right mediastinal displacement, smaller right hemithorax and elevation of the right hemidiaphragm). The patient mentioned that he suffered from mild dyspnea on exertion and an intermittent chest pain. Physical examination revealed diminished breath sounds at the lung bases. He underwent a chest-CTand the findings were suggestive of right UPAA. MRIangiography confirmed the diagnosis and also excluded the presence of other congenital anomalies of the heart or the great vessels of the thorax. UPAA is an extremely rare congenital anomaly with an incidence of1:200,000, usually diagnosed during the first year of life. Many times it remains asymptomatic until adulthood where it is diagnosed incidentally due to an abnormal chest x-Ray performed for another reason. Pneumon 2006,19(2):141-145.