Idiopathic hypercalciuria (IHC) is defined by an urinary calcium excretion greater than or equal to 0.10 mmol/kg body weight/day on a free diet in the absence of hypercalcemia. Pak's classification into absorptive and renal forms of IHC is no longer accepted as such. The now proposed "operational" classification of IHC separates dietary IHC, where calcium excretion falls below 0.07 mmol/kg BW/day on moderate dietary calcium restriction, from true IHC, where urinary calcium excretion remains above this value while on a 600 mg Ca diet, with renal and absorptive "presentations". Etiopathogenic mechanisms of IHC are revisited and appear to be multifactorial. They involve endogenous factors, such as disorders of calcitriol biosynthesis (or receptors), bone resorption and/or calcium membrane transport, whose phenotypic expression is enhanced by extrinsic factors, mainly nutritional, such as high animal protein and salt intake. A protocol of laboratory investigation based on these recent data is proposed, together with a stepped therapeutic approach involving a readjustment of nutritional habits combined, when needed, with thiazide diuretics.