Graft-versus-host disease (GVHD) continues to be a major complication following allogeneic hematopoietic cell transplantation (allo-HCT) with high morbidity and mortality. Corticosteroids are the first-line treatment for GVHD; however, a substantial number of patients go on to require second-line treatment where no single therapeutic modality has been proven to be the most effective. Extracorporeal photopheresis (ECP) is an efficient and established therapy for cutaneous T-cell lymphoma, GVHD, rejection after solid organ transplantation and various autoimmune diseases. Although large randomized trials are limited, there is compelling cumulative data on the efficacy of ECP for GVHD, and the response rates, especially for cutaneous involvement, are encouraging. ECP has an excellent safety profile, a well-documented steroid-sparing effect, proven survival benefit and overall quality-of-life improvement. In many institutions, ECP is commonly regarded as the preferred second-line treatment for GVHD.