Renal angiomyolipoma is a benign mesenchymatous tumour. Whether isolated or associated with phacomatoses, they are histologically identical and the hypothesis which suggests that isolated angiomyolipomas represent a forme fruste or tuberose sclerosis is attractive. The tumour is benign and resembles a carcinoma clincally and radiologically, to such an extent as to lead to confusion. Improved knowledge and more detailed study of radiological documents should avoid their always being, in the words of R. Couvelaire" a constant operative or histological surprise". However whilst there remains no doubt as to its benign nature, the association of true malignant tumours is possible and even seems frequent, which takes us back to the starting point and, given the difficulty of the pre-operative differential diagnosis with a carcinoma; we prefer to opt for extended nephrectomy when operation is indicated.