Incidence of malignancies in patients on dialysis is higher than in the comparable population. The topic is discussed from different points of view: A. Malignancy as a cause of renal failure (renal and urinary tract tumors, von Hippel- Lindau disease, Wilms tumor, multiple myeloma, tumors that compress urinary tract). B. Treatment of malignancies may result in renal failure and dialysis (nephrectomy, tumor-lysis syndrome, postradiation fibrosis, direct toxic effect of chemotherapy). C. Dialyzed patients are in higher risk of malignancies, especially those of the kidney and urinary tract but also of pharynx and larynx, thyroid gland etc. The following factors may play some roles: the basic disease, (e.g. analgesic and Balcan nephropathies, China Herba nephropathy etc.), changed metabolic milieu with retention of carcinogens, deficiency of selenium and other substances, acquired renal cysts, compromised immunity, decreased “wash-effect“ in oligo-anuria and possible influence of dialysis itself (contact with phtalates, ethylenoxide, nitrosamines etc.). D. Special problems in diagnostics of malignancies. Controversial validity of s.c. „tumor markers“ is mentioned. Among the causes of death in dialyzed patients cardiovascular and infectious diseases predominate. The active search for renal and urinary tract tumors should be performed. All other diagnostic procedures depend on the individual patient’s risk profile. E. Methods of renal substitution are used in the treatment of malignancies (e.g. dialysis in the tumor-lysis syndrome, plasma filtration to remove paraproteins, intraperitoneal administration of chemotherapy similar to peritoneal dialysis approach). F. Malignant tumors and dialysis – some ethical problems. Withdrawal of dialysis in severely suffering patients should be approved by an informed patient and followed by maximal palliative therapy including palliative ultrafiltration if threat of lung edema occurs.

        Key words: renal failure, dialysis, malignancies.