The incidence of non-Hodgkin's lymphoma was analysed in over 70,000 kidney transplant recipients and over 10,000 heart, heart-lung or lung transplant recipients. An increased incidence of lymphomas during the first posttransplant year was observed in cadaver kidney recipients as compared to related kidney recipients, in thoracic organ recipients as compared to kidney recipients, in heart-lung recipients as compared to heart or lung recipients, in patients transplanted in North America as compared to patients transplanted in Europe, in patients receiving cyclosporine in combination with azathioprine as compared to patients with other immunosuppressive regimens, and in patients receiving ATG/ALG or monoclonal OKT3 for rejection prophylaxis.