Unilateral hypoplasia of a pulmonary artery (UHPA) is a rare condition that is usually associated with cardiac anomalies in childhood. In the absence of cardiac anomalies, patients may not be diagnosed until respiratory symptoms develop. We present two patients who were diagnosed as having isolated unilateral right pulmonary artery hypoplasia, one a woman aged 80 years, the other, a man aged 55 years. To our knowledge, woman is the oldest patient with UHPA in the English medical literature. Awareness of this condition may contribute to the early recognition of these cases and planning of appropriate treatment.