In its typical form renal carcinoma shows at imaging as a solid, heterogeneous and vascularized mass deforming the kidney; its CT scan appearance is usually very suggestive. Atypical forms (small or cystic carcinomas, large carcinomas with exorenal extension, haemorrhagic carcinomas) mainly raise problems of characterization; the lesional image is always suspicious at CT or combined US, CT and MRI examinations. The detection of small tumours primarily rests on CT with contrast injection, a technique which is more sensitive (94%) than all other techniques. Among non-tumoral lesions which may look like renal carcinomas, some pseudotumoral inflammatory lesions and suspicious atypical cysts often require histological examination. With the exception of angiomyolipoma with its fat content detectable at CT or MRI, there is no truly specific criterion to differentiate benign tumour from cancer. The diagnosis of renal carcinoma extension primarily rests on MRI. In a number of cases the results are so inadequate for the study of renal veins and caval vein that a complementary exploration of these veins by Doppler ultrasonography or MRI must be requested.