The present article reports a rare case of isolated primary left lung agenesis who presented with the history of recurrent respiratory infections. Lung agenesis is an uncommon entity resulting due to non-proliferation of the lung bud. The agenesis may be complete or partial depending upon the time of proliferative arrest. It may be isolated or associated with organ anomalies. In complete agenesis, there is no development of pulmonary vasculature or lung parenchyma, however, there may be rudimentary bronchus (as in the present case). The rudimentary bronchus becomes the site of impacted secretions which result in recurrent infections. The lung aplasia or hypoplasia may be primary or secondary. The secondary hypoplasia is due to some other anomalies like congenital diaphragmatic hernia which hampers the noemal development of the lung. The lung aplasia may be unilateral or bilateral. The bilateral lung aplasia is incompatible with life.