Ciclosporin A (CsA) is a cyclic undecapeptide of fungal origin endowed with immunosuppressive properties but also active on cells outside the immune system, especially epidermal and hair-follicle keratinocytes. Its wide clinical use for the prevention of organ graft rejection has led to the discovery of its beneficial effect in some dermatoses, mainly psoriasis, by a mechanism that still remains largely speculative. Treatment with CsA induces cutaneous and extracutaneous side-effects; whereas some of these are relatively benign and regressive upon treatment discontinuation, others (notably nephrotoxicity) are potentially serious and may require CsA withdrawal. The topical use of CsA has generally proven ineffective, but ongoing studies will hopefully result in the discovery of forms (or analogues) that are active in local applications.