Changes in glomerular capillaries, mensangial structures and tubules are caused by the sickling process. In young patients tubules are caused by the sickling process. In young patients there is an increase of the renal blood-flow but the flow passing in the vasa recta is reduced. A by-pass gives a congestion of the vessels situated at the cortico-medullary junction and around the renal pelvis. All this gives 3 main clinical syndromes: hematuria, nephrotic syndrome and renal insufficiency.