Increasingly potent immunosuppressive agents have dramatically reduced the incidence of rejection of transplanted organs while increasing susceptibility to opportunistic infections and cancer. This article reviews general concepts for the management of transplantation-associated infections and discusses recent advances and challenges. Increasingly potent immunosuppressive agents have increased susceptibility to opportunistic infections. This article reviews general concepts for the management of transplantation-associated infections and discusses recent advances and challenges. Increasingly potent immunosuppressive agents have dramatically reduced the incidence of rejection of transplanted organs while increasing patients' susceptibility to opportunistic infections and cancer. 1 , 2 At the same time, patterns of opportunistic infections after transplantation have been altered by routine antimicrobial prophylaxis for Pneumocystis carinii (also called P. jirovecii ) and cytomegalovirus. These patterns have also been altered by the emergence of new clinical syndromes (e.g., polyomavirus type BK nephropathy) and by infections due to organisms with antimicrobial resistance. New quantitative molecular and antigen-based microbiologic assays detect previously unrecognized transplantation-associated pathogens such as lymphocytic choriomeningitis virus. These assays are used in . . .