An increased incidence of malignancy has been reported in transplant recipients. The pathogenesis of this increase was originally attributed to immunosuppressive therapy. However, not all tumours are increased in proportion to their occurrence in the general population-75% of reported tumours are lymphoproliferative or carcinoma of the skin, lip, or cervix. This cannot be explained by impaired immunosurveillance, and alternative hypotheses must be considered. 90% of transplant recipients develop clinical or serological evidence of herpesvirus infection. Herpesviruses have been implicated in the pathogenesis of lymphoproliferative tumours and carcinoma of the skin and cervix. They can remain in latent form and be reactivated by allogeneic stimulation and/or immunosuppression. These viruses localise to skin, cervix, and neural tissue-i.e., exactly those sites where cancer develops in transplant patients. Herpesvirus infections in association with the presence of an allogeneic graft in an immunosuppressed patient may be responsible for the increased incidence of both lymphoproliferative tumours and carcinoma of the skin, lip, and cervix in the transplant recipient.