Background: The management of systemic sclerosis remains unsatisfactory. Thus far, the action of extracorporeal photopheresis (ECP) in severe systemic scleroderma has been evaluated in short-term studies, and only limited experience has been obtained with long-term application. Objective: The aim of the present study was to evaluate prospectively the long-term effect of ECP in a group of 16 patients suffering from severe scleroderma, showing visceral involvement and progressive clinical course. Methods: Fourteen patients with systemic scleroderma involving several organs, 1 with CREST syndrome and another with scleroderma-myositis overlap syndrome were treated with ECP over a period of 6–45 months. In 3 cases, γ-IFN was additionally administered. Skin and visceral involvement were assessed by evaluating a series of clinical criteria and results from laboratory, imaging and functional tests. Results: Overall, clear improvement was encountered in 6 patients, mixed response in 2, stable disease in 3 and continuing progressive course in 5 patients. Four out of 6 patients with improvement were treated with ECP early after onset of scleroderma (≤2 years), whereas all patients with a progressive course under ECP had had scleroderma for longer than 2 years. Immunosuppressive drugs previously administered could be reduced or fully withdrawn under ECP treatment in 5 patients, but additional oral medication was introduced in 4 patients due to disease progression. Addition of γ-IFN to ECP did not reveal further benefit. No side-effects were recorded under ECP treatment. Conclusions: Based on this observation, we believe that long-term ECP represents an effective treatment modality in severe scleroderma particularly when started early, with stabilization of the disease course and partial remission of the cutaneous findings, whereas visceral involvement, if present, may rarely improve.