The normal inflammatory response seen with an invasion of microbes is reduced in transplant recipients due to the use of immunosuppressive medication. This often makes diagnosis of infectious diseases difficult. Urinary tract infections, pneumonia, wound infections and infections related to foreign material may occur in the first few weeks after renal transplantation. One to four months after renal transplantation opportunistic infections and cytomegalovirus infections are common. From four months on there are only minor differences with respect to infectious diseases between organ transplant recipients and the normal population. Successful treatment of infectious disease in organ transplant recipients depends on early diagnosis and adequate choice of therapy.