We report the case of an iatrogenic gas embolism related to a subclavian vein catheterization complicated by a preexisting partial pneumothorax. Catheterization was indicated because of a septic shock due to nosocomial pneumonia. Five days after the catheterization, the haemodynamics and gas exchanges of the patient worsened. A transthoracic echography showed gas embolism in the right heart related to a right partial pneumothorax. A leak between the pleura and the left subclavian vein was diagnosed. The insertion of a chest tube stopped the airflow, by suppressing the pneumothorax.