Cyclosporin is a selective immunosuppressant that has a variety of applications in medical practice. Like phenytoin and the calcium channel blockers, the drug is associated with gingival overgrowth. This review considers the pharmacokinetics, pharmacodynamics, uses and unwanted effects of cyclosporin, in particular the action of the drug on the gingival tissues. Clinical and cell culture studies suggest that the mechanism of gingival overgrowth is a result of an interaction between the drug and its metabolites with susceptible gingival fibroblasts. Plaque-induced gingival inflammation appears to enhance this interaction.