Unilateral pulmonary agenesis is a rare congenital anomaly whose aetiology is not completely known. Vitamin A deficiency, viral agents, or genetic factors are discussed. The incidence was estimated at 1 in 10,000-15,000 autopsies by several authors. Associated malformations, mainly affecting the cardiovascular, gastrointestinal, and musculoskeletal system influence the prognosis of patients as does the location of the missing lung. We report the implantation of a tissue-expander in a three-months-old infant suffering from a right-sided lung agenesis associated with sinus-venosus defect. Other malformations were excluded by sonographic methods. Mediastinal shift with dextropositio cordis in compensatory emphysema of the left lung and frequent infections were the cardinal symptoms. These led to cardiopulmonary decompensation twice. The implantation of the tissue-expander was performed following an aortopexy, which was only temporarily successful. This method allows the filler to be adapted with age to the pleural volume by instillation of sterile saline solution via a microport. Whether or not thorax deformities and scoliosis will be prevented cannot be predicted exactly at this time.