Mycophenolate mofetil (MMF), a widely used immunosuppressant in organ transplantation, is a recent addition to the therapeutic armamentarium of autoimmune and inflammatory skin disorders in dermatology. We describe 5 patients with moderate to severe chronic plaque psoriasis and 6 patients with psoriatic arthritis that was refractory to conventional systemic and/or topical antipsoriatic treatment who were treated with MMF monotherapy (2 g/d) in a 10-week study. Although MMF was tolerated well in all patients, only patients with moderate psoriasis and psoriatic arthritis improved with therapy, whereas patients with severe psoriasis did not respond to MMF. Although MMF seems to be effective and safe for blistering autoimmune diseases and pyoderma gangrenosum, our data do not allow optimistic statements on the use of MMF in severe plaque-stage psoriasis. However, MMF may develop into an interesting therapeutic alternative for patients with psoriatic arthritis. (J Am Acad Dermatol 2000;42:835-7.)