Chest  Xray  findings  of  unilateral  opacification  of  hemithorax  with  mediastinal shift  towards  the  affected  side  may  prompt  the  differential  diagnoses  of  complete  lung atelectasis , suspected  foreign  body  aspiration , bronchial  mass  lesions . We  must  also consider  the  rare  congenital  condition  of  pulmonary  underdevelopment, which  includes  pulmonary  agenesis , aplasia  and  hypoplasia. We  report  a  case  of  20 years  old  female with  left  sided  pulmonary  aplasia.