Postoperative morbidity remains a nightmare (although vivid), both for the patient and the surgeon. One phantasmagorical idea would be to give the patient a « magic potion » preoperatively aiming at eliminating the risk of postoperative complication. The purpose of the present review is to summarize the current knowledge on the potential benefits of immunonutrition administered to urological cancers patients. After a brief summary on the role of immunity in cancer surveillance and treatment, the rationale about administrating oral nutritional supplements able to modulate the patient's immune system before cystectomy for bladder cancer will be highlighted.