Extracorporeal photopheresis (ECP) has been used for over 30 years in the treatment of erythrodermic cutaneous T-cell lymphoma (CTCL) and over 20 years for chronic graft-versus-host disease (cGVHD). The lack of prospective randomized trials has led to different centres having different patient selection criteria, treatment schedules, monitoring protocols and patient assessment criteria. ECP for CTCL and cGVHD is available only at six specialized centres across the U.K. In the recent Improving Outcomes Guidance the National Institute for Health and Clinical Excellence endorsed the use of ECP for CTCL and because of the complexity of treatment supported its use in specialized centres and also suggested the need for expansion of this service. In 2005 consultants and senior nurses from all U.K. sites and from Scandinavia formed a Photopheresis Expert Group. This group's first aim was to produce a consensus statement on the treatment of CTCL and cGVHD with ECP using evidence-based medicine and best medical practice, in order to standardize ECP eligibility, assessment and treatment strategies across the U.K.