Cyclosporine is a potent immunosuppressive agent with no appreciable effect on the bone marrow and a selective inhibitory effect on helper T cells. Oral cyclosporine was first used to prevent organ rejection but also has been reported to be effective in other disorders. In cutaneous diseases that respond to oral cyclosporine helper T cells appear to be involved in their pathogenesis. This article reviews the cutaneous diseases that have been treated with cyclosporine and its pharmacology and side effects. Two significant adverse side effects are renal dysfunction and hypertension, both of which are reversible when short-term low-dose (less than 5 mg/kg per day) oral cyclosporine is discontinued. Lymphoma is unlikely in an otherwise healthy patient who has received low-dose oral cyclosporine for limited periods. The use of oral cyclosporine in any patient should be carefully considered in terms of the risk/benefit ratio and needs to be carried out under close medical supervision. In view of the limited experience with cyclosporine in dermatology, whenever possible its use should be confined to formal clinical studies with established protocols and guidelines. Further controlled studies need to be performed to evaluate the efficacy of low-dose cyclosporine in many dermatoses and its side-effect profile, particularly over the long term.