A six-month-old female infant, first born out of nonconsangunious marriage was brought with fever of 3 days and history of fast breathing and refusal to feed for one day with history of cough, cold on and off since one month for which treatment was taken on outpatient basis with a local practitioner and no investigations done.Antenatal and perinatal history were uneventful with baby being term with birth weight of 2.6 kg and no Neonatal Intensive Care Unit (NICU) admissions, developmental milestones were normal and immunized till date. The mother was operated for atrial septal defect during her childhood.On examination, the baby was irritable, tachypnoeic with nasal flaring, intercostal and subcostal retractions and grunting. The SpO 2 was 90% in room air at the time of admission. Systemic examination revealed crepitations bilateral lung fields and air entry was reduced on left side with tachycardia and no murmurs or gallops.Her initial blood tests showed haemoglobin of 10g/dl and leucocytosis with neutrophilic predominance and arterial blood gases showed hypoxia for which oxygen was delivered Non Re- Isolated Unilateral hypoplasia or agenesis of a branch of pulmonary artery is very rare. It is usually seen associated with congenital heart diseases such as tetralogy of Fallot, atrial septal defect, coarctation of the aorta, right aortic arch, truncus arteriosus, patent ductus arteriosus and pulmonary atresia. It occurs as a result of lack of embryological development of either the left or right sixth aortic arch and has been found to present itself with various clinical manifestations as during childhood it presents as contralateral pulmonary hypertension and in adults as haemoptysis. Early diagnosis and early surgical indication avoids the evolution of pulmonary hypertension to unfavourble state of more severe and progressive degrees and also prevents the development of pulmonary systemic collateral circulation, which is mainly responsible for subsequent haemoptysis in the adulthood. We hereby, report the case of an infant who presented with features of lower respiratory tract infection and later diagnosed as isolated congenital hypoplasia of left pulmonary artery and hence planned for proper follow-up for early surgery thereby preventing complications in the future. KeywordsBreather Mask (NRBM) and SpO 2 of 99% was maintained. Chest x-ray taken [ Further chest computed tomography [Table/ Fig-3a,b] showed a hypoplastic left lung along with left pulmonary artery hypoplasia. There was reduced vascularity of the left lung. The right pulmonary artery was dilated. Computed Tomography (CT) Thorax had incidentally picked up agenesis of left lobe of thyroid [Table /Fig-4]. FreeT4 (0.92ng/dl) and T3 levels (3.4pg/ml) were normal but Thyroid Stimulating Hormone (TSH) level was 7.67uIU/ml slightly above the range (0.8-7.09) so, she was not started on any medications but was counseled for radionucleotide scan which the patient refused. The patient was treated symptomatically and her pneumonia resolved. She improved gradual...