RESUMEN
Urine is a complex balanced solution containing dissociated and non-dissociated solutes. Any variation in urine saturation grade (number of crystals dissolved in a volume of urine), urinary pH and the concentration of crystallization inhibitors can break the normal existing balance and lead to urolithiasis. In the present article we analyze the principal mechanisms (absorptive, renal, resorptive) of hypercalciuria. It will be also shown how heredity directly influences the clinical aspects of cystine, xanthine and oxalate lithiasis and how diet, in association with metabolic disorders, interferes in uric acid and oxalate stone formation. Finally, we report on the roles of urinary tract malformations, urinary tract infections and drugs in the clinical characterization of urolithiasis.