A severe or lengthy disturbance of immunity favors the development of malignant tumors. The increased incidence of lymphomas, leukemias and certain carcinomas in cases of congenital immunodeficiency, as well as of Kaposi's sarcoma and certain lymphomas in the acquired immunodeficiency syndrome (AIDS) are well known. In transplantees, patients undergoing immunosuppressive treatment for autoimmune disorders and cancer patients receiving chemotherapy, the occurrence of secondary neoplasias represents a phenomenon with a specific profile. We have seen 14 solid tumors in patients who were immunosuppressed for one of the 3 above-mentioned reasons. It is a heterogeneous group, both in terms of patient profile and tumor localisation. However, there are certain characteristics of these tumors which distinguish them from similar ones arising in the general population. The advent of more aggressive immunosuppressive therapies, the constant increase in organ transplants and the development of new cancer treatment modalities which influence the patients immune systems explain the importance of this phenomenon. Thus one must constantly be wary of these unusual tumors which occur independently of age and usual risk factors.