Transplantation is the transfer (engraftment) of human cells, tissues or organs from a donor to a recipient with the aim of restoring function(s) in the body. When transplantation is performed between different species, e.g. animal to human, it is named xenotransplantation.The complications of transplantation of all organs are either technical or related to the immunosuppressive therapy. Technical complications are relatively uncommon in renal and cardiac transplantation, but still are a feature of liver and especially pancreatic transplantation. The major complications related to immunosuppression, either directly or indirectly, are infection, ischemic heart disease and cancer. Viral infections, particularly cytomegalovirus (CMV) infection, remain the most prominent of the post-transplant infections, but more exotic infections are seen from time to time, e.g. Aspergillus, Pneumocystis carinii, tuberculosis, and clinicians must be aware of this possibility in these immunosuppressed patients.