A report is made of a rare case of Wilms' tumour which simulated clinically a syndrome of `right heart failure', as found in some cases of Ebstein's disease. The clinical, radiological, and electrocardiographic study led to the suspicion of this type of malformation. The cine-angiographic study revealed two important facts: the impossibility of approaching the inferior vena cava with opaque material injected into the azygos vein and a filling defect of the right atrium. The post-mortem study revealed the presence of a Wilms' tumour of the right kidney which extended into the inferior vena cava and into the right atrium without producing metastases. This seems to be the first case of this peculiar course of a Wilm's tumour which has grown into the right atrium, resulting in this bizarre clinical picture.