We report a case of Sweet's syndrome which responded to treatment with cyclosporin 4 mg/kg/day. Cyclosporin is effective in the treatment of many dermatoses, and although the immunosuppressive effects of cyclosporin are mainly attributed to inhibition of T-lymphocyte proliferation, it has also been shown to affect the functions of both neutrophils and monocytes. Possible mechanisms of action of cyclosporin in Sweet's syndrome are discussed.