Malignancies developed in 141 organ transplant recipients treated with cyclosporine. The cancers showed important differences from those seen following conventional immunosuppressive therapy (CIT). They appeared an average of 20 months after cyclosporine and 60 months after CIT. Non-Hodgkin's lymphomas (NHLs) were the most common tumors, being 41% compared with 12% in CIT patients. They appeared an average of 11 months after transplantation compared with an average of 42 months after CIT. Unlike CIT patients they more often involved lymph nodes, more frequently involved the small intestine, rarely involved the brain, and were more likely to regress after reduction of immunosuppressive therapy. Skin cancers (15% of cancers) were much less common than in CIT patients (40%). Kaposi's sarcomas were more common (8% vs. 3%). In this small series there was a surprising frequency of endocrine-related cancers and renal cell carcinomas. Only 8 patients (6%) were treated with cyclosporine exclusively. The neoplasms probably are not specific to cyclosporine therapy but appear to be a complication of immunosuppression per se.