The authors report two cases of primary non-Hodgkin's malignant lymphoma of the bladder. In contra with secondary site, which are not rare, primary malignant lymphomas of the bladder wall are exceptional. Urinary symptoms are varied and nonspecific. These tumours cannot be distinguished from other bladder tumours on the basis of their radiological or endoscopic appearance. Only histology provides the diagnosis. The pathophysiological hypotheses are discussed. Treatment is mainly based on chemotherapy. Endoscopic drainage procedures are sometimes useful, as in one of the reported cases.