This chapter is based on the study of data collected by Cincinnati Transplant Tumor Registry (CTTR) and the available literature published by both North American and European organ transplant centers. It reviews the characteristics of the most important de novo malignancies in organ allograft recipients. The most frequent cancers in transplant recipients are skin and lip cancer, solid organ malignancies, and post-transplant lymph proliferative disorder (PTLD). Two epidemiological studies have shown a 20- to 40- fold increased incidence of hepatocellular carcinoma (HCC) in transplant recipients compared with age-matched controls. Sarcomas, breast carcinoma, bladder, and bowel cancers are particularly seen after transplantation. Skin cancer is the second most common malignancy after PTLD, and melanomas comprised 16% of all skin cancers in children compared with 5% among adults. Understanding the increased risk of malignancy of transplant recipients, careful surveillance and screening for selected malignancy should be undertaken.