Background: Effective treatment modalities for systemic sclerosis, a life-threatening and disabling disease, are still lacking. Possible efficacy of photopheresis has been reported in several studies. Because of the complexity of the treatment, placebo-controlled trials are difficult to perform. Objective: We investigated the effect of photopheresis on clinical parameters (skin score and internal organ functions), immunologic parameters, and quality of life. Methods: Nineteen patients with progressive systemic sclerosis of less than 5 years’ duration were randomized into 2 groups. One group (group A) received photopheresis for 1 year, the other group (group B) received no treatment at all. After 1 year the groups switched (crossover design). Photopheresis was performed on 2 consecutive days every 4 weeks; the psoralens were administered parenterally. The main outcome parameter was the skin score after 1 year of treatment compared with that of the control group. Results: The average skin score improved with 5.4% (standard error [SE], 20.8%) in group A and deteriorated with 4.5% (SE, 13.8%) in group B (not significant; P = .71). Before crossover, the average increase in skin score was 5.3% (means of entire group). No change was observed in other clinical parameters. Approximately 1 year after crossover, the skin score reversed to what would have been expected with an average increase of 5.3% per year. There was also no effect on immunologic parameters. Quality of life did not change during treatment. Conclusion: We were not able to show that photopheresis, performed as described above, is an effective treatment in systemic sclerosis. The difference in average skin score was statistically and clinically insignificant. Despite the small sample size, we concluded that the magnitude of the observed changes is too small to justify photopheresis as a regular treatment. (J Am Acad Dermatol 1999;41:915-22.)