Among the many adverse effects induced by immunosuppressive drugs, cancers are a major cause of morbidity and mortality. This review is based on the most recent clinical data. Epidemiological studies and cancer registries have consistently shown an increased risk of malignancies in transplant patients although the calculated risk (4-500-fold increase) differs markedly between studies essentially because of differences in methodologies and selection of patients. Skin and lip cancers, lymphomas and Kaposi's sarcomas are the main types of cancer in these patients. A number of risk factors have been identified, such as latent viral infections, the treatment regimen and the level of immunosuppression. The increasing use of immunosuppressive drugs in nontransplant patients is useful to delineate more accurately the consequences of mild-to-moderate immunosuppression.