Idiopathic hypercalciuria is one of the most commonly diagnosed metabolic disorders in paediatric and adult patients with urolithiasis. Increased urinary calcium excretion is defined as >4 mg/kg per day. The degree of hypercalciuria can be also estimated based on calcium/creatinine ratio, which is calculated from the morning urine sample. Symptoms of hypercalciuria are nonspecific and may include e.g. abdominal pain, haematuria, recurrent urinary tract infections, leukocyturia or dysuria. The disorder primarily leads to formation of urinary deposits. Three types of hypercalciuria, i.e. absorptive, renal and resorptive, were distinguished based on Pak’s test. The pathogenesis of idiopathic hypercalciuria probably involves both genetic and environmental factors. It is likely that the disease is polygenic in nature, with a varying expression of multiple genes among patients. It is believed that patients with idiopathic hypercalciuria have an increased number of vitamin D receptors or show higher susceptibility to this compound. Diet is another factor affecting the degree of hypercalciuria and the dynamics of urolithiasis. It also seems that adequate vitamin D supplementation can reduce the predisposition to form calcium crystal deposits. It is increasingly postulated that absorptive, renal and resorptive types of hypercalciuria represent different, alternately occurring manifestations of the same disease. Furthermore, it should be emphasised that urolithiasis and idiopathic hypercalciuria are associated with decreased bone density, which is observed in all patient populations, including children.