We present the case of a young boy with Dent's disease, identified as having a mutation in the kidney-specific chloride-proton antitransporter CLCN5 during investigation for nephrotic-range proteinuria. He went on to develop growth hormone deficiency and was treated with recombinant growth hormone. He later presented acutely with hepatorenal failure and thrombotic occlusion of the middle and right hepatic veins consistent with a diagnosis of Budd-Chiari syndrome, which required a prolonged period of intensive care. The diagnosis of Dent's disease should be considered early in boys with nephrotic-range proteinuria in the absence of clinical oedema and hypoalbuminaemia to allow for the timely introduction of strategies, such as a high-citrate diet, to preserve renal function. The measurement of urinary β-2 microglobulin has been shown by this case to be a more reliable and specific marker of tubular dysfunction than the urinary retinol-binding protein.