Extra-corporeal photopheresis (ECP) is known as safe ultimate treatment option for chronic lung allograft dysfunction (CLAD). Here, we report the first case of ECP as "second-line" immunomodulatory therapy early post-transplant in an adult patient undergoing lung transplantation for severe chronic thromboembolic pulmonary hypertension, complicated by impaired consciousness due to idiopathic hyperammonemia resulting in recurrent hypercapnic respiratory failure. ECP was initiated twice weekly on post-transplant day 25 and standard triple immunosuppression reduced. Within 2 weeks, the clinical status improved. ECP has been continued every 4 weeks after discharge. At 1 year post-transplant, ECP was stopped as maintenance immunosuppression was reached. We recommend to consider the immunomodulatory effect of ECP as "second line" immunomodulatory therapy in cases where standard immunosuppression causes severe collateral damage. ECP is able to assist prevention of allograft rejection in conjunction with reduced levels of standard immunosuppression, even in the early period following lung transplantation.